This list is largely uncomplete since indexation, structure factors extraction, direct and Patterson methods, refinement by the Rietveld method... are part of the whole process. Some of the following publications may contain tests on previously known structures. Some methods proposing an alternative to equipartition at the stage of structure factors extraction, Monte Carlo, model building approaches, etc, are listed. New methods for single crystals which could be soon translated into methods for powders are also partly listed. The classification is questionable, since "global optimization", "direct space", "simulated annealing", etc may be the subject of a same unique paper. Anyway, here is the list !

Search among papers

- Indexing
- "|Fobs|" extraction
- Direct methods / Patterson
- Monte Carlo / Simulated annealing / Direct space / Real Space / Global optimization
- Maximum entropy / Likelihood
- Genetic algorithm
- Grid search
- Structure prediction
- Other

VISSER JW

A FULLY AUTOMATIC PROGRAM FOR FINDING THE UNIT
CELL FROM POWDER DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1969, Vol
2, pp 89-95

WERNER, PE; ERIKSSON, L; WESTDAHL, M

TREOR, A SEMI-EXHAUSTIVE TRIAL-AND-ERROR POWDER
INDEXING PROGRAM FOR ALL SYMMETRIES

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1985, Vol
18, pp 367-370

DE WOLFF PM

J. APPL. CRYST., 1968, Vol 1, pp 108-

SMITH GS; SNYDER RL

FN - CRITERION FOR RATING POWDER DIFFRACTION
PATTERNS AND EVALUATING THE RELIABILITY OF
POWDER-PATTERN INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1979, Vol
12, pp 60-65

BOULTIF, A; LOUER, D

INDEXING OF POWDER DIFFRACTION PATTERNS FOR LOW-SYMMETRYLATTICES
BY THE SUCCESSIVE DICHOTOMY METHOD

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1991, Vol
24, pp 987-993

ITO T

X-ray studies on polymorphism, Tokyo : Maruzen,
1950

WERNER PE

Z. kristallogr., 1964, Vol 120, pp 275-

LIPSON H

ACTA CRYSTALLOGRAPHICA, 1949, Vol 2, pp 43-

DE WOLFF PM

ACTA CRYSTALLOGRAPHICA, 1957, Vol 10, pp 590-

TAUPIN D

J. Appl. Cryst., 1973, Vol 6, 380-385

HESSE R

ACTA CRYSTALLOGRAPHY, 1948, Vol 1, pp 200-

LOUER, D; VARGAS, R

AUTOMATIC INDEXATION OF POWDER DIAGRAMS BASED
ON SUCCESSIVE DICHOTOMIES

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1982, Vol
15, pp 542-545

TAUPIN D

J. APPL CRYST., 1968, Vol 1, pp 178-

ITO T

NATURE, LONDON, 1949, Vol 164, pp 755-

WERNER PE

DETERMINATION OF UNIT-CELL DIMENSIONS FROM INACCURATE
POWDER DIFFRACTION DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1976, Vol
9, pp 216-219

BENOIT PH

ADAPTATION TO MICROCOMPUTER OF THE APPLEMAN-EVANS
PROGRAM FOR INDEXING AND LEAST-SQUARES REFINEMENT
OF POWDER-DIFFRACTION DATA FOR UNIT-CELL DIMENSIONS

AMERICAN MINERALOGIST 1987, Vol 72, pp 1018-1019

KOHLBECK F; HORL EM

INDEXING PROGRAM FOR POWDER PATTERNS ESPECIALLY
SUITABLE FOR TRICLINIC, MONOCLINIC AND ORTHORHOMBIC
LATTICES

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1976, Vol
9, Iss FEB1, pp 28-33

RUNGE C

Z. PHYSIK, 1917, Vol 18, pp 509-

SHIRLEY R

Data accuracy for powder indexing

Natl. Bur. Stand. (US) Spec. Publ. N°567,
1980, pp 361-382

TAKAKI Y; TANIGUCHI T; HORI K

PROGRAM PACKAGE FOR OBTAINING UNIT-CELL CONSTANTS
AND POSSIBLE SPACE-GROUPS FROM X-RAY-POWDER
DIFFRACTION DATA

NIPPON SERAMIKKUSU KYOKAI GAKUJUTSU RONBUNSHI-JOURNAL
OF THE CERAMIC SOCIETY OF JAPAN 1993, Vol
101, Iss 3, pp 373-376

ALBERTI A

USE OF STRUCTURE FACTORS IN REFINEMENT OF UNIT-CELL
PARAMETERS FROM POWDER DIFFRACTION DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1976, Vol
9, Iss OCT1, pp 373-374

WU E

POWD, AN INTERACTIVE PROGRAM FOR POWDER DIFFRACTION
DATA INTERPRETATION AND INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1989, Vol
22, pp 506-510

KOHLBECK F; HORL EM

TRIAL AND ERROR INDEXING PROGRAM FOR POWDER PATTERNS
OF MONOCLINIC SUBSTANCES

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1978, Vol
11, Iss FEB, pp 60-61

SERYKH VP

UNAMBIGUOUS INDEXING OF POWDER PATTERNS FROM
MONOCLINIC AND ORTHORHOMBIC CRYSTALS

KRISTALLOGRAFIYA 1975, Vol 20, Iss 6, pp 1170-1174

MIGHELL AD

REDUCED CELL - ITS USE IN IDENTIFICATION OF CRYSTALLINE
MATERIALS

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1976, Vol
9, Iss DEC1, pp 491-498

JAMARD C; TAUPIN D; GUINIER A

BULL. SOC. FRANC. MINER. CRIST., 1966, Vol 89,
pp 312-

SMITH GS; KAHARA E

AUTOMATED COMPUTER INDEXING OF POWDER PATTERNS
- MONOCLINIC CASE

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1975, Vol
8, Iss DEC1, pp 681-683

LOUER D

Automatic Indexing : procedures and applications

NIST Special Publication 846 (1992) pp 92-104

GREIS O

SYSTEMATIC PROCEDURE FOR INDEXING X-RAY POWDER
PATTERNS OF SUPERSTRUCTURE PHASES

MONATSHEFTE FUR CHEMIE 1977, Vol 108, Iss 1,
pp 205-211

PASZKOWICZ W

APPLICATION OF OPTIMIZATION TO POWDER-PATTERN
INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1987, Vol
20, pp 166-172

SMITH GS

ESTIMATING UNIT-CELL VOLUMES FROM POWDER DIFFRACTION
DATA - TRICLINIC CASE

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1976, Vol
9, Iss DEC1, pp 424-428

MIGHELL AD; SANTORO A

GEOMETRICAL AMBIGUITIES IN INDEXING OF POWDER
PATTERNS

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1975, Vol
8, Iss JUN1, pp 372-374

TAUPIN D

INFORMATION IN POWDER PATTERN INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1988, Vol
21, pp 485-489

SHIRLEY R; LOUER D

NEW POWDER INDEXING PROGRAMS FOR ANY SYMMETRY
WHICH COMBINE GRID-SEARCH WITH SUCCESSIVE
DICHOTOMY

ACTA CRYSTALLOGRAPHICA SECTION A 1978, Vol 34,
pp S382-S382

TAUPIN D

ENHANCEMENTS IN POWDER-PATTERN INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1989, Vol
22, pp 455-459

PASZKOWICZ W

INDEXING - PROGRAM FOR INDEXING POWDER PATTERNS
OF CUBIC, TETRAGONAL, HEXAGONAL AND ORTHORHOMBIC
SUBSTANCES ON PERSONAL COMPUTERS

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1989, Vol
22, pp 186-187

WU E

A MODIFICATION OF THE DEWOLFF FIGURE OF MERIT
FOR RELIABILITY OF POWDER PATTERN INDEXING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1988, Vol
21, pp 530-535

Cabeza A; Aranda MAG; MartinezLara M; Bruque S

How to solve the problems for the indexation
of complex materials using laboratory powder diffraction:
Application to metal phosphonates

EUROPEAN POWDER DIFFRACTION: EPDIC IV, PTS 1
AND 2 1996, Vol 228, pp 165-170

BAILEY SW

PRACTICAL NOTES CONCERNING THE INDEXING OF X-RAY-POWDERDIFFRACTION
PATTERNS OF CLAY-MINERALS

CLAYS AND CLAY MINERALS 1991, Vol 39, Iss 2,
pp 184-190

Kariuki BM; Belmonte SA; McMahon MI; Johnston
RL; Harris KDM; Nelmes RJ

A new approach for indexing powder diffraction
data based on whole-profile fitting and global optimization
using a genetic algorithm

JOURNAL OF SYNCHROTRON RADIATION 1999, Vol 6,
pp 87-92

Paszkowicz W

Application of the smooth genetic algorithm for
indexing powder patterns - Tests for the orthorhombic
system

EUROPEAN POWDER DIFFRACTION: EPDIC IV, PTS 1
AND 2 1996, Vol 228, pp 19-24

CERNIK RJ

INDEXING UNIT CELLS FROM SYNCHROTRON X-RAY-POWDER
DIFFRACTION DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 277-280

ZABOLOTNYI VA; OVCHINNIKOV VE; SOLOVYEVA LP; SHCHEDRIN
BM PROGRAMS FOR POWDER X-RAY-PATTERNS INDEXING

KRISTALLOGRAFIYA 1983, Vol 28, Iss 1, pp 51-55

ISHIDA T; WATANABE Y

A CRITERION METHOD FOR INDEXING UNKNOWN POWDER
DIFFRACTION PATTERNS

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 1982, Vol 160,
Iss 1-2, pp 19-32

YAO T; JINNO H

COMPUTER-PROGRAMS FOR INDEXING X-RAY-POWDER PATTERNS

NIPPON KAGAKU KAISHI 1980, Iss 4, pp 529-536

Ferraris G; Prencipe M

A warning in indexing triclinic powder diffraction
data

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 1998, Vol 213,
Iss 2, pp 82-84

SERYKH VP; VERKHOROBIN LF

FULL-PROFILE POWDER PATTERNS INDEXING

KRISTALLOGRAFIYA 1983, Vol 28, Iss 6, pp 1199-1200

SERYKH VP

THE USE OF EXTINCTIONS IN POWDER PATTERNS INDEXING
PROGRAMS

KRISTALLOGRAFIYA 1982, Vol 27, Iss 5, pp 994-994

SERYKH VP; SERCHENKO AI

PROGRAM FOR INDEXING A POWDER X-RAY-DIFFRACTION
PATTERN OF ORTHORHOMBIC CRYSTALS ON A MIR
DIGITAL-COMPUTER

KRISTALLOGRAFIYA 1976, Vol 21, Iss 4, pp 820-821

Altomare A; Giacovazzo C; Guagliardi A; Moliterni
AGG; Rizzi R; Werner PE

New techniques for indexing: N-TREOR in EXPO

JOURNAL OF APPLIED CRYSTALLOGRAPHY 2000, Vol
33, pp 1180-1186

Paszkowicz, W

Properties of a genetic algorithm extended by
a random self-learning

operator and asymmetric mutations:
A convergence study for a task of

powder-pattern indexing

ANALYTICA CHIMICA ACTA 566, 2006, 81-98.

Genetic algorithms represent a powerful global-optimisation
tool

applicable in solving tasks of high
complexity in science, technology,

medicine, communication, etc. The
usual genetic-algorithm calculation

scheme is extended here by introduction
of a quadratic self-learning

operator, which performs a partial
local search for randomly selected

representatives of the population.
This operator is aimed as a minor

deterministic contribution to the
(stochastic) genetic search. The

population representing the trial
solutions is split into two equal

subpopulations allowed to exhibit
different mutation rates (so called

asymmetric mutation). The convergence
is studied in detail exploiting a

crystallographic-test example of
indexing of powder diffraction data of

orthorhombic lithium copper oxide,
varying such parameters as imitation

rates and the learning rate. It
is shown through the averaged (over the

subpopulation) fitness behaviour,
how the genetic diversity in the

population depends on the mutation
rate of the given subpopulation.

Conditions and algorithm parameter
values favourable for convergence in

the framework of proposed approach
are discussed using the results for

the mentioned example. Further data
are studied with a somewhat

modified algorithm using periodically
varying mutation rates and a

problem-specific operator. The chance
of finding the global optimum and

the convergence speed are observed
to be strongly influenced by the

effective mutation level and on
the self-learning level. The optimal

values of these two parameters are
about 6 and 5%, respectively. The

periodic changes of mutation rate
are found to improve the explorative

abilities of the algorithm. The
results of the study confirm that the

applied methodology leads to improvement
of the classical genetic

algorithm and, therefore, it is
expected to be helpful in constructing

of algorithms permitting to solve
similar tasks of higher complexity.

Louer, D Boultif, A

Indexing with the successive dichotomy method,
DICVOL04

ZEITSCHRIFT FUR KRISTALLOGRAPHIE Suppl. 23, part1,
2006, 225-230.

A new version of the program based on the dichotomy
principle for

powder pattern indexing is reported.
The new facilities of the program

DICVOL04 include a tolerance for
spurious diffraction lines, a

refinement of the zero-point shift
together with that of cell

parameters, an a priori search for
a zero-point offset in the input

data, a reviewing of all available
powder data from the indexing

solution found from, generally,
the first twenty lines. New strategies

have been introduced to limit the
risk to miss a solution. The program

efficiency is shown with many tests.
Additionally, the robustness of

the program with respect to the
minimum of lines required for finding

solutions is presented and examples
of two-phases patterns are used to

test the performance of the program.

Boultif, A

History of the dichotomy method for powder pattern
indexing

POWDER DIFFRACTION 20, 2005, 284-287.

A short history of the developments of the successive
dichotomy method

for powder pattern indexing is presented.
In the first computer powder

indexing programs (P1 and P2), only
high lattice symmetries, down to

orthorhombic, were considered [Louer
and Louer, J. Appl. Crystallogr.

5, 271-275 (1972)]. Later on, an
extension to the monoclinic symmetry

was reported in DICVOL, including
a partition of the volume space to

first search solutions with smaller
unit cell volumes [Louer and

Vargas, J. Appl. Crystallogr. 15,
542-545 (1982)]. However, CPU times

were slow in some monoclinic examples.
A thorough mathematical analysis

resulted in a significant optimization
of the CPU times [Boultif and

Louer, J. Appl. Crystallogr. 24,
987-993 (199 1)]. Simultaneously, the

method is extended to triclinic
lattices. The stages of development of

the various versions of the DICVOL
program are described, with a

particular emphasis on DICVOL91
(Boultif and Louer, 1991) and DICVOL04

[Boultif and Louer, J. Appl. Crystallogr.
37, 724-731 (2004)]. This

article is written to testify to
and emphasize the major role played by

Daniel Louer, who introduced the
successive dichotomy method and

continued to its evolution and optimization
over almost 40 years.

2004

Boultif, A Louer, D

Powder pattern indexing with the dichotomy method

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004,
724-731.

The efficiency of the successive dichotomy method
for powder

diffraction pattern indexing [Louer
& Louer (1972). J. Appl. Cryst. 5,

271-275] has been proved over more
than 30 years of usage. Features

implemented in the new version of
the computer program DICVOL04 include

(i) a tolerance to the presence
of impurity (or inaccurately measured)

diffraction lines, (ii) a refinement
of the 'zero-point' position,

(iii) a reviewing of all input lines
from the solution found from,

generally, the first 20 lines, (iv)
a cell analysis, based on the

concept of the reduced cell, to
identify equivalent monoclinic and

triclinic solutions, and (v) an
optional analysis of input powder data

to detect the presence of a significant
'zero-point' offset. New search

strategies have also been introduced,
e. g. each crystal system is

scanned separately, within the input
volume limits, to limit the risk

of missing a solution characterized
by a metric lattice singularity.

The default values in the input
le have been extended to 25 A for the

linear parameters and 2500 A 3 for
the cell volume. The search is

carried out exhaustively within
the input parameter limits and the

absolute error on peak position
measurements. Many tests with data from

the literature and from powder data
of pharmaceutical materials,

collected with the capillary technique
and laboratory monochromatic

X-rays, have been performed with
a high success rate, covering all

crystal symmetries from cubic to
triclinic. Some examples reported as

'difficult' cases are also discussed.
Additionally, a few

recommendations for the correct
practice of powder pattern indexing are

reported.

Le Bail, A

Monte Carlo indexing with McMaille

POWDER DIFFRACTION 19, 2004, 249-254.

A Monte Carlo code for indexing powder diffraction
patterns is

presented. Cell parameters are generated
randomly and tested against an

idealized powder profile generated
from the extracted d's and I's.

Mighell, AD

Ambiguities in powder indexing: Conjunction of
a ternary and binary

lattice metric singularity in the
cubic system

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE
OF STANDARDS AND

TECHNOLOGY 109, 2004, 569-579.

A lattice metric singularity occurs when unit
cells defining two (or

more) lattices yield the identical
set of unique calculated d-spacings.

The existence of such singularities,
therefore, has a practical and

theoretical impact on the indexing
of powder patterns. For example, in

experimental practice an indexing
program may find only the lower

symmetry member of a singularity.
Obviously, it is important to

recognize such cases and know how
to proceed. Recently, we described:

(1) a binary singularity involving
a monoclinic and a rhombohedral

lattice in a subcell-supercell relationship
and (2) a second type of

singularity - a ternary singularity
- in which two of the three

lattices are in a derivative composite
relationship. In this work, we

describe a ternary lattice metric
singularity involving a cubic P, a

tetragonal P, and an orthorhombic
C lattice. Furthermore, there is a

binary singularity, involving a
hexagonal P and orthorhombic P lattice,

which is characterized by a set
of unique d-spacings very close to that

of the ternary singularity. The
existence of such singularities is more

common than once thought and requires
a paradigm shift in experimental

practice. In addition singularities
provide opportunities in material

design as they point to highly specialized
lattices that may be

associated with unusual physical
properties.

Habershon, S Cheung, EY
Harris, KDM Johnston, RL

Powder diffraction indexing as a pattern recognition
problem: A new

approach for unit cell determination
based on an artificial neural

network

JOURNAL OF PHYSICAL CHEMISTRY A, 108, 2004, 711-716.

An artificial neural network, in combination
with local optimization,

is shown to be an effective approach
for determining unit cell

parameters directly from powder
diffraction data. The viability of this

new approach is initially demonstrated
using simulated powder

diffraction data. Subsequently,
the successful application of the

method to determine unit cell parameters
is illustrated for two

materials using experimental powder
X-ray diffraction data recorded on

a standard laboratory diffractometer.

2003

Neumann, MA

X-Cell: a novel indexing algorithm for routine
tasks and difficult cases

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003,
356-365.

X-Cell is a novel indexing algorithm that makes
explicit use of

systematic absences to search for
possible indexing solutions from

cells with low numbers of calculated
reflections to cells with high

numbers of reflections. Space groups
with the same pattern of

systematic absences are grouped
together in powder extinction classes,

and for a given peak number range
an independent search is carried out

in each powder extinction class.
The method has the advantage that the

correct cell is likely to be found
before the rapid increase of

possible solutions slows down the
search significantly. A successive

dichotomy approach is used to establish
a complete list of all possible

indexing solutions. The dichotomy
procedure is combined with a search

for the zero-point shift of the
diffraction pattern, and impurity peaks

can be dealt with by allowing for
a user-defined portion of unindexed

reflections. To rank indexing solutions
with varying numbers of

unindexed reflections, a new figure
of merit is introduced that takes

into account the highest level of
agreement typically obtained for

completely incorrect unit cells.
The indexing of long and flat unit

cells is facilitated by the possibility
to search for rows or zones in

reciprocal space first and then
to use the lattice parameters of the

dominant row or zone in the unit-cell
search. The main advantages of

X-Cell are robustness and completeness,
as demonstrated by a validation

study on a variety of compounds.
The dominant phase of phase mixtures

can be indexed in the presence of
up to 50% of impurity peaks if

high-quality synchrotron data are
available.

Coelho, AA

Indexing of powder diffraction patterns by iterative
use of singular

value decomposition

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003,
86-95

A fast method for indexing powder diffraction
patterns has been

developed for large and small lattices
of all symmetries. The method is

relatively insensitive to impurity
peaks and missing high d-spacings:

on simulated data, little effect
in terms of successful indexing has

been observed when one in three
d-spacings are randomly removed.

Comparison with three of the most
popular indexing programs, namely

ITO, DICVOL91 and TREOR90, has shown
that the present method as

implemented in the program TOPAS
is more successful at indexing

simulated data. Also significant
is that the present method performs

well on typically noisy data with
large diffractometer zero errors.

Critical to its success, the present
method uses singular value

decomposition in an iterative manner
for solving linear equations

relating hkl values to d-spacings.

Florence, AJ Baumgartner, B
Weston, C Shankland, N

Kennedy, AR Shankland,
K David, WIF

Indexing powder patterns in physical form screening:
Instrumentation

and data quality

JOURNAL OF PHARMACEUTICAL SCIENCES 92, 2003,
1930-1938.

Two multisample laboratory powder diffractometers
have been evaluated

for the purpose of pattern indexing
in the context of physical form

screening. Both diffractometers
utilise foil transmission geometry,

primary monochromated radiation,
and a position-sensitive detector.

Data collected from six compounds
(sotalol hydrochloride,

hydroflumethiazide, verapamil hydrochloride,
captopril, clomipramine

hydrochloride, and famotidine) showed
good angular resolution (FWHM as

small as ca. 0.06degrees) and lattice
parameters were easily obtained

using the indexing program DICVOL-91.
The extent of preferred

orientation in each pattern was
estimated using the DASH implementation

of the March-Dollase function and
is most evident with clomipramine

hydrochloride and famotidine. Otherwise,
the data compare favorably

with reference capillary data sets.
In conclusion, where there is a

requirement to analyze 20-30 samples
per day, with an emphasis on

obtaining the high-quality data
that are important in pattern

recognition and imperative in indexing,
the combination of foil

transmission geometry, primary monochromated
radiation, plus a

position-sensitive detector is highly
effective. The data also afford

opportunities for crystal structure
determination.

Hageman, JA Wehrens, R
De Gelder, R Buydens, LMC

Powder pattern indexing using the weighted crosscorrelation
and genetic

algorithms

JOURNAL OF COMPUTATIONAL CHEMISTRY 24, 2003,
1043-1051.

X-ray diffraction is a powerful technique for
investigating the

structure of crystals and crystalline
powders. Unfortunately, for

powders, the first step in the structure
elucidation process,

retrieving the unit cell parameters
(indexing), is still very critical.

In the present article, an improved
approach to powder pattern indexing

is presented. The proposed method
matches peak positions from

experimental X-ray powder patterns
with peak positions from trial cells

using a recently published method
for pattern comparison (weighted

crosscorrelation). Trial cells are
optimized with Genetic Algorithms.

Patterns are not pretreated to remove
any existing zero point shift, as

this is determined during optimization.
Another improvement is the peak

assignment procedure. This assignment
is needed for determining the

similarity between lines from trial
cells and experiment. It no longer

allows calculated peaks to be assigned
twice to different experimental

peaks, which is beneficial for the
indexing process. The procedure

proves to be robust with respect
to false peaks and accidental or

systematic absensences of reflections,
and is successfully applied to

powder patterns originating from
orthorhombic, monoclinic, and

triclinic compounds measured with
synchrotron as well as with

conventional laboratory X-ray diffractometers.

PAWLEY GS

UNIT-CELL REFINEMENT FROM POWDER DIFFRACTION
SCANS

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1981, Vol
14, pp 357-361

LE BAIL A; DUROY H; FOURQUET JL

ABINITIO STRUCTURE DETERMINATION OF LISBWO6 BY
X-RAY-POWDER DIFFRACTION

MATERIALS RESEARCH BULLETIN 1988, Vol 23, Iss
3, pp 447-452

A. Le Bail,

Extracting structure factors from powder diffraction
data by iterating full pattern profile fitting,

NIST Special Pubication
846 (1992) 213.

RODRIGUEZCARVAJAL J

RECENT ADVANCES IN MAGNETIC-STRUCTURE DETERMINATION
BY NEUTRON POWDER DIFFRACTION

PHYSICA B 1993, Vol 192, Iss 1-2, pp 55-69

TORAYA H

WHOLE-POWDER-PATTERN FITTING WITHOUT REFERENCE
TO A STRUCTURAL MODEL - APPLICATION TO X-RAY-POWDER
DIFFRACTOMETER DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1986, Vol
19, pp 440-447

Altomare, A; Burla, MC; Cascarano, G; Giacovazzo,
G; Guagliardi, A; Moliterni, AGG; Polidori, G

EXTRA: A program for extracting structure factor
amplitudes from powder diffraction data.

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1995, Vol
28, pp 842-846

JANSEN, J; PESCHAR, R; SCHENK, H

ON THE DETERMINATION OF ACCURATE INTENSITIES
FROM POWDER DIFFRACTION DATA .1. WHOLE-PATTERN
FITTING WITH A LEAST-SQUARES PROCEDURE

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1992, Vol
25, pp 231-236

JANSEN, J; PESCHAR, R; SCHENK, H

ON THE DETERMINATION OF ACCURATE INTENSITIES
FROM POWDER DIFFRACTION DATA .2. ESTIMATION
OF INTENSITIES OF OVERLAPPING REFLECTIONS

JOURNAL OF APPLIED CRYSTALLOGRAPHY, 1992, Vol
25, pp 237-243

SIVIA DS; DAVID WIF

A BAYESIAN-APPROACH TO EXTRACTING STRUCTURE-FACTOR
AMPLITUDES FROM POWDER DIFFRACTION DATA

ACTA CRYSTALLOGRAPHICA SECTION A 1994, Vol 50,
pp 703-714

DAVID WIF

THE PROBABILISTIC DETERMINATION OF INTENSITIES
OF COMPLETELY OVERLAPPING REFLECTIONS IN POWDER
DIFFRACTION PATTERNS

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1987, Vol
20, pp 316-319

ESTERMANN MA; GRAMLICH V

IMPROVED TREATMENT OF SEVERELY OR EXACTLY OVERLAPPINGBRAGG-REFLECTIONS
FOR THE APPLICATION OF DIRECT-METHODS TO POWDER DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 396-404

TORAYA H

ARRAY-TYPE UNIVERSAL PROFILE FUNCTION FOR POWDER
PATTERN FITTING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1990, Vol
23, pp 485-491

Altomare A; Cascarano G; Giacovazzo C; Guagliardi
A; Moliterni AGG; Burla MC; Polidori G

On the number of statistically independent observations
in a powder diffraction pattern

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1995, Vol
28, pp 738-744

Carrozzini B. Giacovazzo C. Guagliardi A. Rizzi
R. Burla MC. Polidori G.

SOLVING CRYSTAL STRUCTURES FROM POWDER DATA .3.
THE USE OF THE PROBABILITY DISTRIBUTIONS FOR ESTIMATING THE |F|S

J. Appl. Crystallogr. 30(1997) 92-97.

Altomare A; Foadi J; Giacovazzo C; Moliterni AGG;
Burla MC; Polidori G

Solving crystal structures from powder data.
IV. The use of patterson information for estimating the
|F|'s

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1998, Vol
31, pp 74-77

Rius J; Sane J; Miravitlles C; Amigo JM; Reventos
MM; Louer D

Determination of crystal structures from powder
diffraction data by direct methods: Extraction of
integrated intensities from partially overlapping Bragg reflections

ANALES DE QUIMICA 1996, Vol 92, Iss 4, pp 223-227

Altomare-A; Giacovazzo-C; Moliterni-AGG; Rizzi-R

A random procedure for the decomposition of a
powder pattern in EXPO.

J. Appl. Cryst. 34 (2001) 704-709

B. Grzeta & H. Toraya,

Powder-pattern-fitting methods in structure determination,

Croatica Chemica Acta 67 (1994) 273-288.

Lasocha W. Schenk H.

A SIMPLIFIED, TEXTURE-BASED METHOD FOR INTENSITY
DETERMINATION OF OVERLAPPING REFLECTIONS IN POWDER DIFFRACTION

Journal of Applied Crystallography 30 (1997)
561-564.

Cerny R.

Powder pattern decomposition with the aid of
preferred orientation - use of the whole Debye-Scherrer ring.

Mater. Sci. Forum 378-381 (2001) 24-29.

Feng, ZJ Dong, C

GENEFP: a full-profile fitting program for X-ray
powder patterns using

the genetic algorithm

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006,
615-617.

GENEFP is a full-profile fitting program, employing
a

fundamental-parameters method, for
Cu-target X-ray powder patterns. In

this program, the Le Bail method
is used to determine integrated

intensities and the genetic algorithm
is used to search for the proper

fundamental parameters. When some
parameters, such as the grain size,

have large uncertainties, the genetic
algorithm has an advantage over

conventional least-squares methods
in finding the global extremum.

Altomare, A Cuocci, C
Giacovazzo, C Moliterni, AGG Rizzi, R

The combined use of Patterson and Monte Carlo
methods for the

decomposition of a powder diffraction
pattern

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006,
145-150.

The success of ab initio crystal structure solution
by powder

diffraction data is strictly related
to the quality of the integrated

intensity estimates. A new method
that is able to improve the pattern

decomposition step has been developed.
It combines the inversion of a

suitably modified Patterson map
with the use of the Hamming codes

[13,10] and [40,36] in order to
explore more decomposition trials. The

new approach has been introduced
in EXPO2005, an updated version of

EXPO2004, and successfully applied
to a set of known organic and

inorganic structures.

2005

Altomare, A Cuocci, C
da Silva, I Giacovazzo, C Moliterni, AGG
Rizzi, R

Full powder pattern decomposition and direct
phasing in EXPO2004: A

statistical study

POWDER DIFFRACTION 20, 2005, 327-333.

Ab initio crystal structure solution by powder
diffraction data is

based on the experimental full pattern
decomposition process: the

resulting structure factor moduli
are used for direct phasing. The

extracted intensity estimates are
scarcely accurate (overlapping,

background, and preferred orientation
are the main causes of the lack

of accuracy), no matter if Le Bail
or Pawley method is adopted:

consequently the structure solution
process is not straightforward. We

have focused our attention on the
relation between the efficiency of

the EXP02004 phasing process and
the various parameters which are

normally used in the full pattern
decomposition process, e.g., the peak

shape function, the number of refinement
cycles, the degree of

overlapping. Different steps of
the phasing process are considered: the

definition of the unit cell, the
determination of the space group, and

the application of direct methods.

2004

Altomare, A Caliandro, R
Cuocci, C da Silva, I Giacovazzo, C

Moliterni, AGG Rizzi,
R

The use of error-correcting codes for the decomposition
of a powder

diffraction pattern

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004,
204-209.

The decomposition of a powder diffraction pattern
consists of the

extraction of the intensities of
the individual reflections from the

experimental profile. The process
is crucial for structure

determination from powder diffraction
data, but its accuracy is limited

by the intrinsic peak overlap. A
substantial improvement is achieved by

considering clusters of reflections
in strong overlap and partitioning

in a systematic way the total intensity
of each cluster among the

constituent reflections. In this
paper, error-correcting codes are used

to explore the set of decomposition
trials obtained by combining the

partitions of various clusters of
overlapping reflections. Linear

ternary codes resulting from modifications
of the Hamming codes [ 13,

10] and [ 40, 36] have been considered
as the most suited for the

present problem. They have been
included in the EXPO program via their

generator matrices. Tests on a set
of experimental powder patterns show

that an efficient decomposition
procedure consists of performing only

27 decomposition trials, determined
as the codewords of an [ndoub, 3]

code, where ndoub is the number
of doublets of strong overlapping

reflections found in the experimental
profile. This allows a reduction

in the number of trials, thus processing
about 2% of the number used in

a previous design of the same procedure,
leading to a reduction of the

total execution time by nearly the
same amount.

2003

Guo, LP Cheng, ZX Han,
FT Liu, Y Zhao, ZX

Simulated annealing method for powder diffraction
pattern decomposition

ACTA PHYSICA SINICA 52, 2003, 2842-2848.

Simulated annealing algorithm was applied in
the decomposition of

neutron and x-ray powder diffraction
pattern. The method described in

this paper has two main advantages:
first, the pattern decomposition

results do not depend on the starting
peak parameters, thus the

difficulty in the choice of initial
solutions, which occurs in fitting

a complex pattern composed of severely
overlapped peaks by a

conventional least-squares profile
fitting method, is overcome;

secondly, it has the ability of
searching for global other than local

optimal solutions, thus can effectively
resolve the multi-solution

problem mathematically, and this
advantage is the most useful when

decomposing complex patterns with
several local optimal solutions. The

computing step is described in detail,
the setting of relative

parameters is discussed, and the
simulated annealing method is compared

with a conventional least-squares
profile fitting method through both

simulated pattern and actual pattern
to demonstrate its unique

advantage in the decomposition,
of, complex pattern. In principle, the

method can also be applied in other
kinds of spectra which can be

described by profile shape function.

Altomare, A Caliandro, R
Cuocci, C Giacovazzo, C Moliterni, AGG
Rizzi, R

A systematic procedure for the decomposition
of a powder diffraction

pattern

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003,
906-913.

Ab initio crystal structure solution from powder
diffraction data can

be attained by means of the two-stage
method: first the integrated

intensities of individual reflections
are extracted from the

experimental profile; then the extracted
intensities are processed by

direct methods to recover their
phase. The efficiency of the

direct-methods process is strongly
affected by the accuracy of the

extracted intensities and this is
a serious drawback for the solution

of organic compounds, where the
presence of light atoms leads to a

rapid decrease of the scattering
at high angles. In order to overcome

this problem, a procedure is proposed
which generates a set of

different intensity partitions for
groups of reflections in strong

overlap: the resulting decomposition
trials are supplied to direct

methods. The procedure is able to
reduce the phase error at the end of

the phasing process by up to 50degrees
and enables the solution of

organic structures with data resolution
not worse than 1.5 Angstrom in

a reasonable computing time. The
procedure has been implemented in the

EXPO program, which makes use of
the Le Bail extraction algorithm.

Peterson, VK

Lattice parameter measurement using Le Bail versus
structural

(Rietveld) refinement: A caution
for complex, low symmetry systems

POWDER DIFFRACTION 20, 2005, 14-17.

The measurement of lattice parameters using the
Le Bail method was

shown to be inappropriate for a
complex, low symmetry, structure, even

with high resolution synchrotron
diffraction data. The method failed as

a result of ambiguous indexing in
the absence of constraints on

diffraction intensities, that arise
when a structural model is used,

combined with the large number of
reflections. A caution for the use of

the Le Bail and other whole-powder
pattern decomposition methods is

presented, particularly for high
reflection density data.

Wright, JP

Extraction and use of correlated integrated intensities
with powder

diffraction data

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2005, 791-802.

The transformation of a powder diffraction profile
into a set of

correlated integrated intensities
allows crystallographic calculations

to be performed without modelling
raw diffractometer counts. By

carrying out this transformation
it is possible to preserve the

information about peak overlap without
needing to retain the multitude

of experimental details and description
of the peak shape function. An

implementation is described which
allows problems of significant size

to be tackled. Least squares refinement.
issues of data quality and the

generation and importance of free
R-factors are discussed.

Ma, HW Liang, JK Liu,
GY Rao, GH

UACIEM: A new method to extract reliable intensities
of nonequivalent

systematical overlapping reflections
from powder diffraction data

POWDER DIFFRACTION 19, 2004, 333-339.

A new method, namely UACIEM, to extract reliable
intensities of

nonequivalent systematical overlapping
reflections has been proposed

and tested by simulated powder diffraction
data from known crystal

structures. Using both crystallographic
and structural chemistry

information, the method reconstructs
diffraction intensities and solves

a crystal structure through an iterative
procedure. Our study shows

that UACIEM is successful for cases
where more than 30% of the total

scattering power is located with
precision from equivalent systematical

overlapping reflections. The UACIEM
process is not needed when

equivalent systematical overlapping
reflections are sufficient to

reveal a crystal structure. UACIEM
may fail in cases when: (i) only a

small portion of the total scattering
power (e.g., less than 7%) can be

located, and (ii) most of the total
scattering power (e.g., 95%) is

located, but the atomic coordinates
are not accurately known. The

UACIEM method is superior to the
simple equipartition methods for

nonequivalent systematical overlapping
reflections.

Ma, HW Liang, JK

A new approach to extract reliable intensities
of non-equivalent

systematical overlapping reflections
from powder diffraction data

ACTA PHYSICA SINICA 53, 2004, 829-834.

A new approach to extract reliable intensities
from systematical

non-equivalent overlapping reflections
has been proposed and tested by

simulated powder diffraction pattern
of known structures. By using both

crystallographic and structural
chemistry knowledge, the IDM-UAIC

reconstructs the intensities and
solves the structure through an

iterative procedure. The results
show that IDM-UAIC succeeds when more

than 30% of the total scattering
power can be located in a reasonable

precise from the equivalent systematical
overlapping reflections. The

IDM-UAIC procedure is superior to
the simple equi-partition methods for

the nonequivalent systematical overlapping
reflections while it is

equivalent to simple equi-partition
methods for the equivalent

systematical overlapping reflections.

Tucker, MG Dove, MT Keen,
DA

Application of the reverse Monte Carlo method
to crystalline materials

JOURNAL OF APPLIED CRYSTALLOGRAPHY 34, 2001,
630-638.

An implementation of the reverse Monte Carlo
(RMC) method for the study

of crystalline materials from polycrystalline
neutron total scattering

data is presented. The new feature
is that explicit account is taken of

the intensities of Bragg peaks,
which are extracted from the data using

the Pawley method. The use of Bragg
peaks ensures that the RMC models

reproduce both the long-range and
the short-range order reflected in

the experimental data. The relative
effects of different contributions

to the data sets in the RMC method
are assessed and successful

applications are illustrated using
the quartz and cristobalite

polymorphs of silica as examples.

Space group determination

Altomare, A Caliandro, R
Camalli, M Cuocci, C da Silva, I

Giacovazzo, C Moliterni,
AGG Spagna, R

Space-group determination from powder diffraction
data: a probabilistic

approach

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004,
957-966.

Experimental powder diffraction diagrams, once
indexed and decomposed

into single diffraction intensities,
can be submitted to statistical

analysis for the determination of
space-group symmetry. A new algorithm

is illustrated, which is able to
provide, on a quantitative basis, a

probability value for each extinction
symbol compatible with the

previously established lattice symmetry.
The algorithm has been

implemented in EXPO2004 [Altomare,
Caliandro, Camalli, Cuocci,

Giacovazzo, Moliterni & Rizzi
( 2004). J. Appl. Cryst. 37, 1025 - 1028]

and has been successfully tested
using a large set of experimental data.

Markvardsen, AJ David, WIF
Johnson, JC Shankland, K

A probabilistic approach to space-group determination
from powder

diffraction data

ACTA CRYSTALLOGRAPHICA SECTION A 57, 2001, 47-54.

An algorithm for the determination of the space-group
symmetry of a

crystal from powder diffraction
data, based upon probability theory, is

described. Specifically, the relative
probabilities of different

extinction symbols are assessed
within a particular crystal system. In

general, only a small number of
extinction symbols are relatively

highly probable and a single extinction
symbol is often significantly

more probable than any other. Several
examples are presented to

illustrate this approach.

A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori & M. Camalli,

SIRPOW.92

J. Appl. Cryst. 27 (1994) 435-436.

C. Cascarano, L. Favia & C. Giacovazzo,

SIRPOW.91- a direct-methods package optimized
for powder data,

J. Appl. Cryst. 25 (1992) 310-317.

Altomare A; Burla MC; Camalli M; Carrozzini B;
Cascarano GL; Giacovazzo C; Guagliardi A; Moliterni
AGG; Polidori G; Rizzi R

EXPO: a program for full powder pattern decomposition
and crystal structure solution

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 339-340

Altomare A. Burla MC. Cascarano G. Giacovazzo
C. Guagliardi A. Moliterni AGG. Polidori G.

EARLY FINDING OF PREFERRED ORIENTATION - APPLICATIONS
TO DIRECT METHODS

Journal of Applied Crystallography. 29(1996)
341-345.

J. Jansen, R. Peschar & H. Schenk,

Application of direct methods to powder data.
A weighting scheme for intensities in the optimal symbolic addition program
SIMPEL88,

Z. Kristallogr. 206 (1993) 33-43.

W. Prandl,

Phase determination and Patterson maps from multiwavelength
powder data,

Acta Cryst. A46 (1990) 988-992.

W. Prandl,

Phase determination from X-ray powder diffraction
data II. Partial Patterson maps and the localization of anomalously scattering
atoms,

Acta Cryst. A50 (1994) 52-55.

Burger K. Prandl W. Doyle S.

STRUCTURE DETERMINATION FROM POWDER DATA USING
ANOMALOUS SCATTERING - DIFFERENCE AND PARTIAL, PATTERSON DENSITIES, AND
PHASES OF STRUCTURE FACTORS

Zeitschrift fur Kristallographie. 212 (1997)
493-505.

Rius J. Miravitlles C. Gies H. Amigo JM.

A tangent formula derived from Patterson-function
arguments. VI. Structure solution from powder patterns with systematic
overlap

J. Appl. Crystallogr. 32(Part 1):89-97, 1999.

Rius-J; Torrelles-X; Miravitlles-C; Ochando-LE; Reventos-MM; Amigo-JM

A tangent formula derived from Patterson-function arguments. VII. Solution
of inorganic structures from powder data with accidental overlap

JOURNAL-OF-APPLIED-CRYSTALLOGRAPHY. OCT 1 2000; 33 Part 5 : 1208-1211

Rius J

XLENS, a direct methods program based on the modulus sum function:
Its application to powder data

POWDER-DIFFRACTION. DEC 1999; 14 (4) : 267-273

Burla, MC Caliandro, R Carrozzini, B
Cascarano, GL De Caro, L

Giacovazzo, C Polidori, G Siliqi,
D

The revenge of the Patterson methods. I. Protein ab initio phasing

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006, 527-535.

Direct methods combined with direct-space refinement procedures are
the

standard tools for ab initio crystal structure solution
of

macromolecules via diffraction data collected up to atomic
or

quasi-atomic resolution. An entirely direct-space approach
is described

here: it includes an automated Patterson deconvolution
method, based on

the minimum superposition function, followed by an effective

direct-space refinement, consisting of cycles of electron
density

modification. The new approach has been implemented in
a new version of

the SIR2004 program and tested on a large set of test
structures

selected from the Protein Data Bank, with data resolution
better than

1.6 angstrom and number of non-hydrogen atoms in the asymmetric
unit up

to 2000. The new procedure proved to be extremely efficient
and very

fast in solving crystal structures with atomic resolution
data and

heavy atoms: their solution and refinement requires a
computing time

roughly comparable with that necessary for solving small-molecule

crystal structures via a modern computer program. It markedly
overcomes

direct methods, even for crystal structures with atomic
data resolution

and heaviest atomic species up to calcium, as well as
for crystal

structures with quasi-atomic data resolution (i.e. 1.2
- 1.6 angstrom).

The Patterson approach proved to be loosely dependent
on the structure

complexity.

Rius, J

Advances and some recent applications of the origin-free modulus sum

function

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2005, 826-832.

Since its discovery, the direct methods origin-free modulus sum

function [Rius, J., Acta Cryst A49 (1993) 406-409] has
been responsible

for the solution of a number of difficult crystal structures
of

minerals and other inorganic compounds from powder diffraction
data.

This is principally due to the efficiency, robustness
and simplicity of

implementation of this phase refinement function. The
first part of the

contribution describes some recent examples on the application
of the

origin-free modulus sum function to complex structures.
In the second

part, a powerful variant of this function is introduced
which

discriminates even better the correct solutions from the
wrong ones.

This is illustrated with its application to single-crystal
data of

three selected organic structures. One of these test structures

contains 317-atom molecules and is regarded as one of
the most

difficult structures to be solved with reciprocal space
direct methods.

This variant could also be useful for those phase refinement
strategies

based on alternating reciprocal- and real-space procedures,
provided

that the weak reflections are known.

Caliandro, R Carrozzini, B Cascarano, GL
De Caro, L

Giacovazzo, C Siliqi, D

Phasing at resolution higher than the experimental resolution

ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY 61, 2005,
556-565.

Limited experimental resolution is a unavoidable feature in

macromolecular crystallography: it may hinder or make
difficult the

determination of the crystal structure. A novel procedure
is presented

which from an approximate electron-density map extrapolates
the moduli

and phases of non-measured reflections beyond and behind
the

experimental resolution limit. Applications to a set of
test structures

show that the extrapolation can be successfully accomplished.
As a

consequence, the phase estimates of the observed reflections
are

subsequently improved and the interpretability of the
corresponding

electron-density map increases. The use of the extrapolated
values for

the non-measured reflections provides additional information
for the

map, which shows a resolution higher than the experimental
resolution.

Rius-Palleiro, J Peral, I Margiolaki, I
Torrelles, X

Solving centrosymmetrical zeolites from powder diffraction data by

combining the direct-methods origin-free modulus sum function
with the

isomorphous replacement technique. X

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 906-911.

A new two-stage strategy for the solution of zeolite crystal structures

with centrosymmetrical frameworks is proposed; this strategy
exploits

the information contained in multiple powder diffraction
patterns. In

the first stage, the structure-directing agent (SDA),
i.e. the template

molecule, is located by combining the isomorphous replacement
technique

with direct methods. In the second stage, the framework
atoms are found

by applying direct methods strengthened with additional
information

coming from the located SDA. All phase refinements are
based on the

maximization of the origin-free modulus sum function as
implemented in

the direct-methods program XLENS [Rius (2004). Z. Kristallogr.
219,

826-832], with data resolution limits equal to 3.2 angstrom
for the

first and 2.21 angstrom for the second stage. The viability
of this new

two-stage strategy is illustrated with the solution of
the novel

zeolite ITQ-32, containing nine Si atoms in the asymmetric
unit, from

synchrotron powder diffraction data. Especially important
is the

confirmation that the intensity differences involved in
the SDA

isomorphous replacement are significantly greater than
the

experimentally measured errors.

2004

Altomare, A Caliandro, R Camalli, M
Cuocci, C Giacovazzo, C

Moliterni, AGG Rizzi, R Spagna,
R Gonzalez-Platas, J

Towards EXPO2005

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2004, 833-837

New procedures have been introduced in EXPO2004 (Altomare. A..

Caliandro, R., Camalli, M., Cuocci, C., da Silva, I.,
Giacovazzo, C.,

Moliterni, A. G. G. & Rizzi, R., J. Appl. Cryst. Submitted)
aiming at

making the solution process more straightforward, particularly
for

cases very resistant to the ab-initio approach.

Altomare, A Caliandro, R Camalli, M
Cuocci, C Giacovazzo, C

Moliterni, AGG Rizzi, R

Automatic structure determination from powder data with EXPO2004

JOURNAL OF APPLIED CRYSTALLOGRAPHY37, 2004, 1025-1028

EXPO2004 is the updated version of the EXPO program [Altomare et al.

(1999). J. Appl. Cryst. 32, 339 - 340]. The traditional
steps of the ab

initio powder solution process are performed automatically:
indexing,

space-group determination, decomposition of the pattern
for extracting

the observed structure-factor moduli, structure solution
by direct

methods, model refinement by Rietveld technique. Special
strategies may

be applied to improve both the estimates of the extracted

structure-factor moduli and the quality of the structure
model. In

addition, the use of special procedures exploiting available

supplementary information on molecular geometry can be
successfully

adopted. The graphical interface has also been improved.

Altomare, A Giacovazzo, C Grazia, A
Moliterni, G Rizzi, R

Direct methods optimised for solving crystal structure by powder

diffraction data: Limits, strategies, and prospects

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND

TECHNOLOGY 109, 2004, 125-132.

ab-initio crystal structure solution by powder diffraction data

requires great efforts because of the collapse of the
experimental

information onto the one dimensional 2theta axis of the
pattern.

Different strategies will be described aiming at improving
the process

of extraction of the integrated intensities from the experimental

pattern in order to make more straightforward the structure
solution

process by direct methods. Particular attention will be
devoted to the

EXPO program. Some of its performance will be analysed
and results will

be shown.

Altomare, A Cuocci, C Giacovazzo, C
Grazia, A Moliterni, G Rizzi, R

Completion of crystal structure with polyhedral coordination: A new

procedure

EUROPEAN POWDER DIFFRACTION EPDIC 8 - MATERIALS SCIENCE FORUM
443-4, 2004, 23-26.

The ab-initio crystal structure solution via powder diffraction data
is

often uncomplete. A recent procedure POLPO [1] aims at
completing a

partial structure model provided by Direct Methods by
exploiting the

prior information on the polyhedral coordination of the
located atoms

(tetrahedral or octahedral) and their connectivity has
been developed.

The POLPO procedure requires that all the cations are
correctly

labelled and rightly located. This condition does not
always occur,

particularly when the data quality is poor. A new method
is described

which is able to locate missing cations and surrounding
anions when the

cation coordination is tetrahedral or octahedral.

Altomare, A Cuocci, C
Giacovazzo, C Moliterni, AGG Rizzi, R

Powder diffraction: the new automatic least-squares
Fourier recycling

procedure in EXPO2005

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006,
558-562.

The Rietveld method is the most widely used approach
for refining

crystal structures from powder diffraction
patterns. It requires

sufficiently accurate structure
models and user skill. A method is

described which is often able to
complete and refine a structure model

by using an automatic least-squares
procedure applicable to reflection

integrated intensities. A weighting
scheme has been devised that is

capable of taking into account the
lower accuracy of the estimates of

the overlapping reflections.

Giacovazzo, C Altomare, A Cuocci, C
Moliterni, AGG Rizzi, R

Completion of crystal structure by powder diffraction data: a new

method for locating atoms with polyhedral coordination

JOURNAL OF APPLIED CRYSTALLOGRAPHY 35, 2002, 422-429.

Ab initio crystal structure solution via powder diffraction data is

often incomplete: frequently, the heavy atoms are correctly
located but

the light-atom positions are usually unreliable. The recently
developed

procedure POLPO [Altomare et al. (2000). J. Appl. Cryst.
33,

1305-1310], implemented in the EXPO program [Altomare
et al. (1999). J.

Appl. Cryst. 32, 339-340], aims at completing a partial
structure model

provided by direct methods by exploiting the prior information
on the

polyhedral coordination of the located atoms (tetrahedral
or

octahedral) and their connectivity. The POLPO procedure
requires that

all the cations are correctly labelled and rightly located.
This

condition does not always occur, particularly when the
data quality is

poor. A new method is described which is able to locate
missing cations

and surrounding anions when the cation coordination is
tetrahedral or

octahedral. The procedure has been successfully checked
on different

test structures.

Altomare, A Cuocci, C Giacovazzo, C
Guagliardi, A Moliterni, AGG Rizzi, R

Real-space technique applied to crystal structure determination from

powder data

JOURNAL OF APPLIED CRYSTALLOGRAPHY 35, 2002, 182-184.

Real-space techniques used for phase extension and refinement in the

modern direct procedures for ab initio crystal structure
solution of

proteins have been optimized for application to powder
diffraction

data. The new process has been implemented in a modified
version of

EXPO [Altomare et al. (1999). J. Appl. Cryst. 32, 339-340].
The method

is able to supply a structural model that is more complete
than that

provided by the standard EXPO program. The model is then
refined via a

diagonal least-squares procedure, but only when the ratio
of the number

of observations to the number of structure parameters
to be refined is

larger than a given threshold.

Altomare, A Giacovazzo, C Ianigro, M
Moliterni, AGG Rizzi, R

Peak labelling in electron density maps from powder data: the use of

crystal chemical information

JOURNAL OF APPLIED CRYSTALLOGRAPHY 35, 2002, 21-27.

Direct methods applied to powder diffraction data often provide

electron density maps of which the quality is usually
affected by

systematic and/or random phase errors, by amplitude truncation
effects

in the series representation of the electron density,
etc. The frequent

incorrect labelling of the peaks can strongly affect the
efficiency of

the procedures used for crystal structure refinement.
For example, the

success of alternative techniques, such as POLPO [Altomare
et al.

(2000). J. Appl. Cryst. 33, 1305-1310], requires that
all the heavy

atoms be positioned and exactly labelled.

DEEM MW; NEWSAM JM

FRAMEWORK CRYSTAL-STRUCTURE SOLUTION BY SIMULATED
ANNEALING - TEST APPLICATION TO KNOWN ZEOLITE STRUCTURES

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 1992,
Vol 114, Iss 18, pp 7189-7198

HARRIS KDM; TREMAYNE M; LIGHTFOOT P; BRUCE PG

CRYSTAL-STRUCTURE DETERMINATION FROM POWDER DIFFRACTION
DATA BY MONTE-CARLO METHODS

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 1994,
Vol 116, Iss 8, pp 3543-3547

CATLOW CRA; BELL RG; GALE JD

COMPUTER MODELING AS A TECHNIQUE IN MATERIALS
CHEMISTRY

JOURNAL OF MATERIALS CHEMISTRY 1994, Vol 4, Iss
6, pp 781-792

Falcioni M; Deem MW

A biased Monte Carlo scheme for zeolite structure
solution

JOURNAL OF CHEMICAL PHYSICS 1999, Vol 110, Iss
3, pp 1754-1766

FREEMAN CM; NEWSAM JM; LEVINE SM; CATLOW CRA

INORGANIC CRYSTAL-STRUCTURE PREDICTION USING
SIMPLIFIED POTENTIALS AND EXPERIMENTAL UNIT CELLS - APPLICATION TO THE
POLYMORPHS OF TITANIUM-DIOXIDE

JOURNAL OF MATERIALS CHEMISTRY 1993, Vol 3, Iss
5, pp 531-535

Engel GE; Wilke S; Konig O; Harris KDM; Leusen
FJJ

PowderSolve - a complete package for crystal
structure solution from powder diffraction patterns

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 1169-1179

CHEETHAM AK; BULL LM

THE STRUCTURE AND DYNAMICS OF ADSORBED MOLECULES
IN MICROPOROUS SOLIDS - A COMPARISON BETWEEN EXPERIMENTS AND COMPUTER-SIMULATIONS

CATALYSIS LETTERS 1992, Vol 13, Iss 3, pp 267-275

Tremayne M; Kariuki BM; Harris KDM

The development of Monte Carlo methods for crystal
structure solution from powder diffraction data: Simultaneous translation
and rotation of a structural fragment within the unit cell

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1996, Vol
29, pp 211-214

Kariuki BM; Zin DMS; Tremayne M; Harris KDM

Crystal structure solution from powder X-ray
diffraction data: The development of monte carlo methods to solve the crystal
structure of the gamma-phase of 3-chloro-trans-cinnamic acid

CHEMISTRY OF MATERIALS 1996, Vol 8, Iss 2, pp
565-569

N. Masciocchi, R. Bianchi, P. Cairati, G. Mezza,
T. Pilati, A. Sironi,

P-RISCON: a real-space scavenger for crystal
structure determination from powder diffraction data,

J. Appl. Cryst. 27 (1994) 426-429.

Andreev YG; Lightfoot P; Bruce PG

A general Monte Carlo approach to structure solution
from powder-diffraction data: Application to poly(ethylene oxide)(3):LiN(SO2CF3)(2)

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1997, Vol
30, pp 294-305

DINUNZIO PE; MARTELLI S; BITTI RR

A MONTE-CARLO ESTIMATE OF CRYSTALLITE-SIZE AND
MICROSTRAIN DISTRIBUTION-FUNCTIONS FROM X-RAY-LINE BROADENING

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1995, Vol
28, pp 146-159

Newsam JM; Freeman CM; Gorman AM; Vessal B

Simulating non-framework cation location in aluminosilicate
zeolites

CHEMICAL COMMUNICATIONS 1996, Iss 16, pp 1945-1946

Harris KDM; Kariuki BM; Tremayne M

Crystal structure solution from powder diffraction
data by the Monte Carlo method

EPDIC 5, PTS 1 AND 2 1998, Vol 278-2, pp 32-37

Andreev YG; Bruce PG

Solving crystal structures of molecular solids
without single crystals: a simulated annealing approach

JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
1998, Iss 24, pp 4071-4080

Takahashi N; Ebihara K; Yoshida K; Nakata T; Ohashi
K; Miyata K

Investigation of simulated annealing method and
its application to optimal design of die mold for orientation of magnetic
powder

IEEE TRANSACTIONS ON MAGNETICS 1996, Vol 32,
Iss 3, pp 1210-1213

Andreev YG; Bruce PG

Solution of flexible structures from powder diffraction
data using a simulated annealing technique

EPDIC 5, PTS 1 AND 2 1998, Vol 278-2, pp 14-19

Coelho AA

Whole-profile structure solution from powder
diffraction data using simulated annealing

JOURNAL OF APPLIED CRYSTALLOGRAPHY 2000, Vol
33, Iss 2, pp 899-908

Tremayne M; Kariuki BM; Harris KDM; Shankland
K; Knight KS

Crystal structure solution from neutron powder
diffraction data by a new Monte Carlo approach incorporating restrained
relaxation of the molecular geometry

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1997, Vol
30, pp 968-974

Montfrooij W; McGreevy RL; Hadfield R; Andersen
NH

Reverse Monte Carlo analysis of powder patterns

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1996, Vol
29, pp 285-290

AREAN CO; GONZALEZ JMR

APPLICATION OF A MONTE-CARLO METHOD TO THE DETERMINATION
OF CATION DISTRIBUTION IN SPINELS BY POWDER DIFFRACTOMETRY

JOURNAL OF SOLID STATE CHEMISTRY 1986, Vol 63,
Iss 2, pp 336-340

Wechsler D; Zsigmond G; Streffer F; Stride JA;
Mezei F

Monte-Carlo simulations for instrumentation at
pulsed and continuous sources

PHYSICA B 2000, Vol 276, pp 71-72

EUTSCH PW; STANIK TD

A TEMPERATURE-DEPENDENT SIMULATION OF THE X-RAY-POWDER
SPECTRUM OF ICE IH USING METROPOLIS MONTE-CARLO SAMPLING

JOURNAL OF CHEMICAL PHYSICS 1986, Vol 85, Iss
8, pp 4660-4666

Mellergard A; McGreevy RL

Reverse Monte Carlo modelling of neutron powder
diffraction data

ACTA CRYSTALLOGRAPHICA SECTION A 1999, Vol 55,
pp 783-789

Di Nunzio PE; Martelli S

Size distribution of single-crystal nanoparticles
by Monte Carlo fitting of wide-angle X-ray scattering peak shape

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 546-548

Altomare A; Giacovazzo C; Guagliardi A; Moliterni
AGG; Rizzi R

Completion of crystal structures from powder
data: the use of the coordination polyhedra

JOURNAL OF APPLIED CRYSTALLOGRAPHY 2000, Vol
33, pp 1305-1310

Toby BH; Khosrovani N; Dartt CD; Davis ME; Parise
JB

Structure-directing agents and stacking faults
in the CON system: a combined crystallographic and
computer simulation study

MICROPOROUS AND MESOPOROUS MATERIALS 2000, Vol
39, Iss 1-2, pp 77-89

Zetterstrom P; McGreevy RL

Improved Monte Carlo program MCGR, for determining
G(r)

PHYSICA B 2000, Vol 276, pp 187-188

Zhukov SG; Chernyshev VV; Babaev EV; Sonneveld
EJ; Schenk H

Application of simulated annealing approach for
structure solution of molecular crystals from X-ray laboratory powder data

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 2001, Vol 216,
Iss 1, pp 5-9

Reinaudi L; Carbonio RE; Leiva EPM

Inclusion of symmetry for the enhanced determination
of crystalline structures from powder diffraction
data using simulated annealing

CHEMICAL COMMUNICATIONS 1998, Iss 2, pp 255-256

Reinaudi L; Leiva EPM; Carbonio RE

Simulated annealing prediction of the crystal
structure of ternary inorganic compounds using symmetry restrictions

JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
2000, Iss 23, pp 4258-4262

Popa NC; Ionita I

The instrumental profile for a neutron powder
diffractometer in focusing geometry

PHYSICA B 2000, Vol 276, pp 192-194

Stoica AD; Popovici M; Yelon WB

Instrumental line shapes in neutron powder diffraction
with focusing monochromators

JOURNAL OF APPLIED CRYSTALLOGRAPHY 2000, Vol
33, pp 137-146

Favre-Nicolin-V; Cerny-R

FOX, 'free objects for crystallography': a modular
approach to ab initio structure determination from powder diffraction

JOURNAL-OF-APPLIED-CRYSTALLOGRAPHY. DEC 2002;
35 Part 6 : 734-743

global-optimization algorithms to solve the structure
by performing trials in direct space.

Seaton CC, Tremayne M.

Differential evolution: crystal structure determination
of a triclinic polymorph of adipamide from powder diffraction data.

Chem Commun 2002:880–881.

The crystal structure of a previously unknown
triclinic polymorph of adipamide has been solved from laboratory X-ray
powder diffraction data using a new direct space global optimisation method
based on differential evolution.

JOHNSTON-John-C; DAVID-William-I-F; MARKVARDSEN-Anders-J;
SHANKLAND-Kenneth

A hybrid Monte Carlo method for crystal structure
determination from powder diffraction data

Acta-crystallographica-Section-A-Foundations-of-crystallography.
2002; 58 (p.5) : 441-447

A. Altomare, C. Cuocci, C. Giacovazzo, A. Guagliardi,
A.G. Moliterni and R. Rizzi,

Real-space technique applied to crystal structure
determination from powder data

J. Appl. Cryst. 35 (2002) 182-184.

Rodriguez-Carvajal,-J.

Magnetic structure determination from powder
diffraction symmetry analysis and simulated annealing

Materials-Science-Forum. 2001; 378-381 pt. 1:
268-73

Le-Bail,-A.

ESPOIR: a program for solving structures by Monte
Carlo analysis of powder diffraction data

Materials-Science-Forum. 2001; 378-381 pt. 1:
65-70

O.J. Lanning, S. Habershon, K.D.M. Harris, R.L.
Johnston, B.M. Kariuki, E. Tedesco and G.W. Turner,

Definition of a 'guiding function' in global
optimization: a hybrid approach combining energy and R-factor in structure
solution from powder diffraction data

Chem. Phys. Letters 317 (2000) 296-303.

Earl, DJ Deem, MW

Parallel tempering: Theory, applications, and
new perspectives

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 7, 2005,
3910-3916.

We review the history of the parallel tempering
simulation method. From

its origins in data analysis, the
parallel tempering method has become

a standard workhorse of physicochemical
simulations. We discuss the

theory behind the method and its
various generalizations. We mention a

selected set of the many applications
that have become possible with

the introduction of parallel tempering,
and we suggest several

promising avenues for future research.

Chong, SY Tremayne, M

Combined optimization using cultural and differential
evolution:

application to crystal structure
solution from powder diffraction data

CHEMICAL COMMUNICATIONS iss 39, 2006, 4078-4080.

The principles of social and biological evolution
have been combined in

a Cultural Differential Evolution
hybrid global optimization technique

and applied to crystal structure
solution.

David, WIF Shankland, K
van de Streek, J Pidcock, E Motherwell, WDS
Cole, JC

DASH: a program for crystal structure determination
from powder

diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006,
910-915.

DASH is a user-friendly graphical-user-interface-driven
computer

program for solving crystal structures
from X-ray powder diffraction

data, optimized for molecular structures.
Algorithms for multiple peak

fitting, unit-cell indexing and
space-group determination are included

as part of the program. Molecular
models can be read in a number of

formats and automatically converted
to Z-matrices in which flexible

torsion angles are automatically
identified. Simulated annealing is

used to search for the global minimum
in the space that describes the

agreement between observed and calculated
structure factors. The

simulated annealing process is very
fast, which in part is due to the

use of correlated integrated intensities
rather than the full powder

pattern. Automatic minimization
of the structures obtained by simulated

annealing and automatic overlay
of solutions assist in assessing the

reproducibility of the best solution,
and therefore in determining the

likelihood that the global minimum
has been obtained.

Charge flipping

Wu, JS Leinenweber, K
Spence, JCH O'Keeffe, M

Ab initio phasing of X-ray powder diffraction
patterns by charge

flipping

NATURE MATERIALS 5, 2006, 647-652.

Determining crystal structures from powder X-
ray diffraction data

remains a challenging problem in
materials science. By embedding a

Le-Bail-like procedure within the
recently discovered charge-flipping

phasing algorithm, an extremely
simple, fast and effective ab initio

method has been developed to determine
phases directly from indexed

powder diffraction patterns. The
algorithm solves the degeneracy

problem by applying spherical averaging
for overlapping Bragg

reflections, while solving the phase
problem by using the Oszlanyi-Suto

charge-flipping algorithm. The processes
of peak decomposition and

phasing are integrated within the
same iteration, and a dynamic support

is used. The Fienup hybrid input-output
algorithm is also incorporated

to minimize stagnation. The ability
of the algorithm to find

structure-factor phases rapidly
is found to assist with the fundamental

problem of degeneracy ( overlapping
reflections) which is intrinsic to

powder diffraction data. Space-group
and chemical-composition

information are not needed as inputs,
and can be determined from the

result. The method is illustrated
using several experimental powder

patterns of indifferent quality.

Palatinus, L

Ab initio determination of incommensurately modulated
structures by

charge flipping in superspace

ACTA CRYSTALLOGRAPHICA SECTION A 60, 2004, 604-610.

The charge flipping algorithm proposed by Oszlanyi
& Suto [Acta Cryst.

(2004), A60, 134-141] for ab initio
reconstruction of crystal

structures is generalized towards
superspace. Its efficiency is

demonstrated by successful reconstruction
of eight known

incommensurately modulated structures
from experimental data. The

output of the charge flipping algorithm
is an electron density with

symmetry P1. The symmetry of the
structure is recovered by locating the

positions of symmetry operators
and averaging the density over the

symmetry-related pixels. The reconstruction
of a modulated structure by

the charge flipping algorithm and
the accuracy of the result is

demonstrated in detail on the modulated
structure of

tetraphenylphosphonium hexabromotellurate(IV)
bis{dibromoselenate(I)}.

2005

Markvardsen, AJ Shankland, K
David, WIF Didlick, G

Characterization of a hybrid Monte Carlo search
algorithm for structure

determination

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005,
107-111.

A hybrid Monte Carlo (HMC) search algorithm has
recently been shown to

be a promising method for structure
determination from powder

diffraction data [ Johnston, David,
Markvardsen & Shankland ( 2002).

Acta Cryst. A58, 441 - 447]. Here,
the performance of the algorithm on

a number of different crystal structures
is investigated as a function

of its control parameters. This
detailed analysis required the use of a

system for distributed computing
in order to keep the calculation times

within a reasonable time frame.
The results obtained confirm previous

findings and a detailed discussion
of the effect of the control

parameters on the efficiency of
the HMC method is provided. The results

suggest a method for setting these
parameters automatically, which is

an essential step if HMC is to find
routine use in the determination of

crystal structures.

Cerny, R Favre-Nicolin, V

FOX: A friendly tool to solve nonmolecular structures
from powder

diffraction

POWDER DIFFRACTION 20, 2005, 359-365.

Structural characterization from powder diffraction
of compounds not

containing isolated molecules but
three-dimensional infinite structure

(alloys, intermetallics, framework
compounds, extended solids) by

direct space methods has been largely
improved in the last 15 years.

The success of the method depends
very much on a proper modeling of the

structure from building blocks.
The modeling from larger building

blocks improves the convergence
of the global optimization algorithm by

a factor of up to 10. However, care
must be taken about the correctness

of the building block, like its
rigidity, deformation, bonding

distances, and ligand identity.
Dynamical occupancy correction

implemented in the direct space
program FOX has shown to be useful when

merging excess atoms, and even larger
building blocks like coordination

polyhedra. It also allows joining
smaller blocks into larger ones in

the case when the connectivity was
not a priori evident from the

structural model. We will show in
several examples of nonmolecular

structures the effect of the modeling
by correct structural units.

Favre-Nicolin, V Cerny, R

FOX, 'free objects for crystallography': a modular
approach to ab

initio structure determination from
powder diffraction

JOURNAL OF APPLIED CRYSTALLOGRAPHY 35, 2002,
734-743.

A new program has been developed for ab initio
crystal structure

determination from powder diffraction
data (X-ray and neutron). It uses

global-optimization algorithms to
solve the structure by performing

trials in direct space. It is a
modular program, capable of using

several criteria for evaluating
each trial configuration (e.g.

multi-pattern). It is also modular
in the description of the crystal

content, with the possibility of
describing building blocks in the

sample, such as polyhedra or molecules,
and with automatic adaptive

handling of special positions and
sharing of identical atoms between

neighbouring building blocks. It
can therefore find the correct

structure without any assumption
about the connectivity of the building

blocks and is suitable for any kind
of material. Several optimization

algorithms (simulated annealing,
parallel tempering) are available,

with the possibility of choosing
the convergence criterion as a

combination of available cost functions.
This program is freely

available for Linux and Windows
platforms; it is also fully 'open

source', which, combined with an
object-oriented design and a complete

developer documentation, ensures
its future evolution.

Favre-Nicolin-, V Cerny, R

A better FOX: using flexible modelling and maximum
likelihood to

improve direct-space ab initio structure
determination from powder

diffraction

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2004, 847-856.

Ab initio structure determination using direct-space
methods, although

relying on an essentially bruteforce
approach, can be greatly improved

through smarter algorithms. The
most basic improvement involves the use

C, of prior information to reduce
the number of configurations

evaluated to find the structure
solution. It is however vitally

important that the parametrization
used to incorporate this prior

information does not reduce the
efficiency with which the configuration

space is explored. We will show
that this can be achieved by defining

molecules and polyhedra through
a set of restraints associated to

dedicated random changes. allowing
to solve structures up to three

times as fast as with the 'standard'
approach where atomic positions

are parametrized directly from bond
lengths, bond angles and dihedral

angles.

To further enhance the efficiency
of the algorithm, it is also possible

to 'tune' the convergence criterion
used to compare the structural

model to the observed diffraction
data (usually chi(2) or R-wp). By

using Maximum Likelihood principles.
it is shown that incorporating the

fact that the model is approximate
in the chi(2) evaluation can improve

the algorithm convergence towards
the structure solution.

Favre-Nicolin, V Cerny,
R

FOX: Modular approach to crystal structure determination
from powder

diffraction

EUROPEAN POWDER DIFFRACTION EPDIC 8 MATERIALS
SCIENCE FORUM 443-4, 2004, 35-38.

Program FOX for ab initio crystal structure determination
from powder

diffraction uses global optimization
algorithms to find the correct

structure by making trials in the
direct space. It is a modular

program, capable of using several
criteria for evaluating each trial

configuration, e.g. combining neutron
and X-ray diffraction patterns.

The program describes the structural
building blocks (polyhedrons,

molecules etc.) with their internal
coordinates (Z-matrices), thus all,

owing natural constraints on interatomic
distances and angles.

Identical atoms shared between neighboring
building blocks, and special

positions are handled with an automatic,
adaptive method (Dynamical

Occupancy Correction). Several algorithms
(Simulated Annealing,

Parallel Tempering) are currently
available. The program is based on an

object-oriented crystallographic
library ObjCryst++ (programming

language c++). The program and the
library are available for Linux and

Windows on http://objcryst.sourceforge.net.
Inorganic and organic

structures with the complexity up
to 26 independents atoms are

routinely solved from laboratory
X-ray, synchrotron or neutron data.

Harris, KDM Habershon, S
Cheung, EY Johnston, RL

Developments in genetic algorithm techniques
for structure solution

from powder diffraction data

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2004, 838-846.

DE X-ray powder diffraction; structure analysis;
structure solution;

genetic algorithm; molecular crystals

ID CRYSTAL-STRUCTURE DETERMINATION; X-RAY-DIFFRACTION;
MONTE-CARLO

APPROACH; R-FACTOR; ACID; ENERGY;
SYSTEM; UNIT

AB This paper presents an overview of developments
that have taken place

in recent years in the genetic algorithm
technique for structure

solution from powder diffraction
data. After a brief resume of the

essential features of the genetic
algorithm technique for structure

solution, the paper highlights recent
developments in fundamental

aspects of the technique, including
the development of parallel

computing concepts, the analysis
of the evolutionary history in genetic

algorithm structure solution calculations
and the combination of energy

information together with the powder
diffraction data in structure

solution. Several examples are also
given to illustrate the application

of the genetic algorithm technique
to solve crystal structures of

different types of organic molecular
materials, including oligopeptides

and multi-component co-crystals.

Brodski, V Peschar, R
Schenk, H

Organa - a program package for structure determination
from powder

diffraction data by direct-space
methods

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005,
688-693.

A new software package has been developed, named
Organa, for ab initio

solution of crystal structures from
powder diffraction data by

direct-space methods. The package
contains energy-guiding Monte Carlo

and grid-search algorithms and is
based on a combined global

minimization of the R factor and
a potential energy function of the

system with the option of local
minimization of the cost function for

each generated trial structure.
Basically, the potential energy

function consists of van der Waals
interactions, but harmonic

potentials can be added to impose
soft distance restraints. The program

was successfully applied to the
structure determination of a series of

melamine phosphate compounds. The
program is freely available ( for all

Windows platforms) from the correspondence
author upon request.

Altomare, A Caliandro, R
Giacovazzo, C Moliterni, AGG Rizzi, R

Solution of organic crystal structures from powder
diffraction by

combining simulated annealing and
direct methods

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003,
230-238.

The ab initio crystal structure solution from
powder diffraction data

can be attempted via direct methods.
If heavy atoms are present, they

are usually correctly located; then
some crystal chemical information

can be exploited to complete the
partial structure model. Organic

structures are more resistant to
direct methods; as an alternative,

their molecular geometry is used
as prior information for Monte Carlo

methods. In this paper, a new procedure
is described which combines the

information contained in the electron
density map provided by direct

methods with a Monte Carlo method
which uses simulated annealing as a

minimization algorithm. A figure
of merit has been designed based on

the agreement between the experimental
and calculated profiles, and on

the positions of the peaks in the
electron density map. The procedure

is completely automatic and has
been included in EXPO; its performance

has been validated and tested for
a set of known molecular structures.

Habershon, S Harris, KDM
Johnston, RL

Development of a multipopulation parallel genetic
algorithm for

structure solution from powder diffraction
data

JOURNAL OF COMPUTATIONAL CHEMISTRY 24, 2003,
1766-1774.

Previously, the genetic algorithm (GA) approach
for direct-space

crystal structure solution from
powder diffraction data has been

applied successfully in the structure
determination of a range of

organic molecular materials. In
this article, we present a further

development of our approach, namely
a multipopulation parallel GA

(PGA), which is shown to give rise
to increased speed, efficiency, and

reliability of structure solution
calculations, as well as providing

new opportunities for further optimizing
our GA methodology. The

multipopulation PGA is based on
the independent evolution of different

subpopulations, with occasional
interaction (e.g., transfer of

structures) allowed to occur between
the different subpopulations.

Different strategies for carrying
out this interpopulation

communication are considered in
this article, and comparisons are made

to the conventional single-population
GA. The increased power offered

by the PGA approach creates the
opportunity for structure determination

of molecular crystals of increasing
complexity.

Brodski, V Peschar, R
Schenk, H

A Monte Carlo approach to crystal structure determination
from powder

diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003,
239-243.

A new direct-space method for ab initio solution
of crystal structures

from powder diffraction data is
presented. The approach consists of a

combined global minimization of
R-wp and the potential energy of the

system. This method was tested on
two organic compounds with known

structure and also applied successfully
in the structure determination

of the previously unknown structure
of melamine pyrophosphate.

Johnston, JC David, WIF
Markvardsen, AJ Shankland, K

A hybrid Monte Carlo method for crystal structure
determination from

powder diffraction data

ACTA CRYSTALLOGRAPHICA SECTION A 58, 2002, 441-447.

A hybrid Monte Carlo algorithm for crystal structure
determination from

powder diffraction data is presented.
The algorithm combines the key

components of molecular dynamics
and Monte Carlo simulations to achieve

efficient sampling of phase space,
allowing the crystal structure of

capsaicin to be determined from
powder diffraction data more

effectively than by a simulated-annealing
approach. The implementation

of the algorithm, the choice of
the simulation parameters and the

performance of the algorithm are
discussed.

Markvardsen, AJ David, WIF
Shankland, K

A maximum-likelihood method for global-optimization-based
structure

determination from powder diffraction
data

ACTA CRYSTALLOGRAPHICA SECTION A 58, 2002, 316-326.

A maximum-likelihood algorithm has been incorporated
into a crystal

structure determination from a powder
diffraction data framework that

uses an integrated-intensity-based
global optimization technique. The

algorithm is appropriate when the
structural model being optimized is

not a complete description of the
crystal structure under study.

Nakamura, H Yamazaki, S
Ohnishi, T Ida, T Toraya, H

The Monte Carlo method for finding missing atoms
in solving crystal

structures from powder diffraction
data without applying a rigid-body

approximation

POWDER DIFFRACTION 16, 2001, 65-70.

The Monte Carlo method is applied to finding
missing atoms in solving

inorganic crystal structures without
applying a rigid-body

approximation. Whole powder patterns
of alpha -SiO2 and Mg2SiO4 were

used for testing a procedure. Four
atoms among the six in the

asymmetric unit of Mg2SiO4 could
be found in the present analysis. The

use of well-refined profile parameters
enhanced the frequency of

correct structure configurations
in the Monte Carlo search. Utilizing

structural information available
for constructing a trial configuration

is also considered to be important
for efficiently searching the

structure solution. A procedure
for assignment of equivalent positions

to respective atoms is presented.
The method can be used as a powerful

tool for finding missing atoms in
a partially solved structure. A

histogram of weighted reliability
index in Monte Carlo calculations is

very informative for evaluating
the performance of the method. (C) 2001

International Centre for Diffraction
Data.

BRICOGNE G

DIRECT PHASE DETERMINATION BY ENTROPY MAXIMIZATION
AND LIKELIHOOD RANKING - STATUS-REPORT AND PERSPECTIVES

ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY
1993, Vol 49, pp 37-60

KUMAZAWA S; KUBOTA Y; TAKATA M; SAKATA M; ISHIBASHI
Y

MEED - A PROGRAM PACKAGE FOR ELECTRON-DENSITY-DISTRIBUTION
CALCULATION BY THE MAXIMUM-ENTROPY METHOD

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 453-457

BRICOGNE G

A MULTISOLUTION METHOD OF PHASE DETERMINATION
BY COMBINED MAXIMIZATION OF ENTROPY AND LIKELIHOOD .3. EXTENSION TO POWDER
DIFFRACTION DATA

ACTA CRYSTALLOGRAPHICA SECTION A 1991, Vol 47,
pp 803-829

GILMORE CJ; HENDERSON K; BRICOGNE G

A MULTISOLUTION METHOD OF PHASE DETERMINATION
BY COMBINED MAXIMIZATION OF ENTROPY AND LIKELIHOOD .4. THE ABINITIO SOLUTION
OF CRYSTAL-STRUCTURES FROM THEIR X-RAY-POWDER DATA

ACTA CRYSTALLOGRAPHICA SECTION A 1991, Vol 47,
pp 830-841

C.J. Gilmore, K. Shankland & G. Bricogne,

Applications of the maximum entropy method to
powder diffraction and electron crystallography,

Proc. R. Soc. Lond. A 442 (1993) 97-111.

K. Shankland & C.J. Gilmore,

The ab initio determination of crystal structures
from their powder diffraction patterns using a combination of entropy maximisation
and likelihood ranking,

Materials Sci. Forum 133/136 (1993) 189.

SAKATA M; MORI R; KUMAZAWA S; TAKATA M; TORAYA
H

ELECTRON-DENSITY DISTRIBUTION FROM X-RAY-POWDER
DATA BY USE OF PROFILE FITS AND THE MAXIMUM-ENTROPY METHOD

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1990, Vol
23, pp 526-534

SAKATA M; UNO T; TAKATA M; HOWARD CJ

MAXIMUM-ENTROPY-METHOD ANALYSIS OF NEUTRON-DIFFRACTION
DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 159-165

GILMORE CJ; HENDERSON AN; BRICOGNE G

A MULTISOLUTION METHOD OF PHASE DETERMINATION
BY COMBINED MAXIMIZATION OF ENTROPY AND LIKELIHOOD .5. THE USE OF LIKELIHOOD
AS A DISCRIMINATOR OF PHASE SETS PRODUCED BY THE SAYTAN PROGRAM FOR A SMALL
PROTEIN

ACTA CRYSTALLOGRAPHICA SECTION A 1991, Vol 47,
pp 842-846

VOIGTMARTIN IG; YAN DH; YAKIMANSKY A; SCHOLLMEYER
D; GILMORE CJ; BRICOGNE G

STRUCTURE DETERMINATION BY ELECTRON CRYSTALLOGRAPHY
USING BOTH MAXIMUM-ENTROPY AND SIMULATION APPROACHES

ACTA CRYSTALLOGRAPHICA SECTION A 1995, Vol 51,
pp 849-868

SHANKLAND K; GILMORE CJ; BRICOGNE G; HASHIZUME
H

A MULTISOLUTION METHOD OF PHASE DETERMINATION
BY COMBINED MAXIMIZATION OF ENTROPY AND LIKELIHOOD .6. AUTOMATIC LIKELIHOOD
ANALYSIS VIA THE STUDENT T TEST, WITH AN APPLICATION TO THE POWDER STRUCTURE
OF MAGNESIUM BORON-NITRIDE, MG3BN3

ACTA CRYSTALLOGRAPHICA SECTION A 1993, Vol 49,
pp 493-501

PAPOULAR RJ; COX DE

MODEL-FREE SEARCH FOR EXTRA-FRAMEWORK CATIONS
IN ZEOLITES USING POWDER DIFFRACTION

EUROPHYSICS LETTERS 1995, Vol 32, Iss 4, pp 337-342

Gilmore C; Dong W; Bricogne G

A multisolution method of phase determination
by combined maximization of entropy and likelihood. VI. The use of error-correcting
codes as a source of phase permutation and their application to the phase
problem in powder, electron and macromolecular crystallography

ACTA CRYSTALLOGRAPHICA SECTION A 1999, Vol 55,
pp 70-83

KUMAZAWA S; TAKATA M; SAKATA M

ON THE SINGLE-PIXEL APPROXIMATION IN MAXIMUM-ENTROPY
ANALYSIS

ACTA CRYSTALLOGRAPHICA SECTION A 1995, Vol 51,
pp 47-53

Sakata M; Takata M

The principle of the maximum entropy method

HIGH PRESSURE RESEARCH 1996, Vol 14, Iss 4-6,
pp 327-333

Elliott JA; Hanna S

A model-independent maximum-entropy method for
the inversion of small-angle X-ray diffraction patterns

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 1069-1083

Knorr K; Madler F; Papoular RJ

Model-free density reconstruction of host/guest
compounds from high-resolution powder diffraction data

MICROPOROUS AND MESOPOROUS MATERIALS 1998, Vol
21, Iss 4-6, pp 353-363

Xie Y; Hao Q

Evaluation of reflection intensities for the
components of multiple Laue diffraction spots by the maximum-entropy method

ACTA CRYSTALLOGRAPHICA SECTION A 1997, Vol 53,
pp 643-648

ESTERMANN MA

SOLVING CRYSTAL-STRUCTURES WITH THE SYMMETRY
MINIMUM FUNCTION

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS
RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED
EQUIPMENT 1995, Vol 354, Iss 1, pp 126-133

Gilmore CJ

Maximum entropy methods in electron crystallography

MICROSCOPY RESEARCH AND TECHNIQUE 1999, Vol 46,
Iss 2, pp 117-129

Burger K; Prandl W

A new type of constraint in the maximum-entropy
method using ambiguous phase information from anomalous-scattering powder
data

ACTA CRYSTALLOGRAPHICA SECTION A 1999, Vol 55,
pp 719-728

Burger K; Cox D; Papoular R; Prandl W

The application of resonant scattering techniques
to ab initio structure solution from powder data using SrSO4 as a test
case

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1998, Vol
31, pp 789-797

Dong W; Gilmore CJ

The ab initio solution of structures from powder
diffraction data: the use of maximum entropy and likelihood to determine
the relative amplitudes of overlapped reflections using the pseudophase
concept

ACTA CRYSTALLOGRAPHICA SECTION A 1998, Vol 54,
pp 438-446

Burger K

Enhanced versions of the maximum entropy program
MEED for X-ray and neutron diffraction

POWDER DIFFRACTION 1998, Vol 13, Iss 2, pp 117-120

Takata M; Nishibori E; Sakata M

Charge density studies utilizing powder diffraction
and MEM. Exploring of high Tc superconductors, C-60 superconductors and
manganites

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 2001, Vol 216,
Iss 2, pp 71-86

Kirihara K; Nakata T; Takata M; Kubota Y; Nishibori
E; Kimura K; Sakata M

Electron-density distribution of approximants
of the icosahedral Al-based alloys by the maximum-entropy method and the
Rietveld refinement

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL
MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 2000, Vol 294, pp 492-495

Dorset DL

Low-resolution direct phase determination in
protein electron crystallography - breaking globular constraints

ACTA CRYSTALLOGRAPHICA SECTION A 2000, Vol 56,
pp 529-535

Armstrong N; Kalceff W

A maximum entropy method for determining column-length
distributions from size-broadened X-ray diffraction profiles

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 600-613

CHEN PY; MOU CY

STATISTICAL-INFERENCE OF DISTRIBUTION OF CRYSTAL
SIZE BY X-RAY-POWDER DIFFRACTION

JOURNAL OF THE CHINESE CHEMICAL SOCIETY 1994,
Vol 41, Iss 1, pp 65-73

DAVID WIF

EXTENDING THE POWER OF POWDER DIFFRACTION FOR
STRUCTURE DETERMINATION

INSTITUTE OF PHYSICS CONFERENCE SERIES 1990,
Iss 107, pp 93-100

ESTERMANN MA; GRAMLICH V

IMPROVED TREATMENT OF SEVERELY OR EXACTLY OVERLAPPING
BRAGG-REFLECTIONS FOR THE APPLICATION OF DIRECT-METHODS TO POWDER DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 396-404

MOENS P; DEVOLDER P; HOOGEWIJS R; CALLENS F; VERBEECK
R

MAXIMUM-LIKELIHOOD COMMON-FACTOR ANALYSIS AS
A POWERFUL TOOL IN DECOMPOSING MULTICOMPONENT EPR POWDER SPECTRA

JOURNAL OF MAGNETIC RESONANCE SERIES A 1993,
Vol 101, Iss 1, pp 1-15

ANTONIADIS A; BERRUYER J; FILHOL A

MAXIMUM-LIKELIHOOD METHODS IN POWDER DIFFRACTION
REFINEMENTS

ACTA CRYSTALLOGRAPHICA SECTION A 1990, Vol 46,
pp 692-711

Tsur Y; Randall CA

Analysis of X-ray powder diffraction data using
the maximum likelihood estimation method

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 2000,
Vol 83, Iss 8, pp 2062-2066

BYROM PG; LUCAS BW

POLISH - A COMPUTER-PROGRAM FOR IMPROVING THE
ACCURACY OF STRUCTURE-FACTOR MAGNITUDES OBTAINED FROM POWDER DATA

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1993, Vol
26, pp 137-139

A. J. Markvardsen, W. I. F. David and K. Shankland

A maximum-likelihood method for global-optimization-based
structure determination from powder diffraction data

Acta Cryst. (2002). A58, 316-326

F. Izumi, A. Yamamoto, N.R. Khasanova, S. Kumazawa,
W.Z. Hu and T. Kamiyama,

Novel techniques of neutron powder diffraction
and their applications to superconducting oxides

Physica C 335 (2000) 239-244.

Program REMEDY : whole pattern-fitting combined
with maximum entropy

Shankland K; David WIF; Csoka T

Crystal structure determination from powder diffraction
data by the application of a genetic algorithm

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 1997, Vol 212,
Iss 8, pp 550-552

Harris KDM; Johnston RL; Kariuki BM

The genetic algorithm: Foundations and applications
in structure solution from powder diffraction data

ACTA CRYSTALLOGRAPHICA SECTION A 1998, Vol 54,
pp 632-645

Kariuki BM; Serrano-Gonzalez H; Johnston RL; Harris
KDM

The application of a genetic algorithm for solving
crystal structures from powder diffraction data

CHEMICAL PHYSICS LETTERS 1997, Vol 280, Iss 3-4,
pp 189-195

WIENKE D; LUCASIUS C; KATEMAN G

MULTICRITERIA TARGET VECTOR OPTIMIZATION OF ANALYTICAL
PROCEDURES USING A GENETIC ALGORITHM .1. THEORY, NUMERICAL SIMULATIONS
AND APPLICATION TO ATOMIC EMISSION-SPECTROSCOPY

ANALYTICA CHIMICA ACTA 1992, Vol 265, Iss 2,
pp 211-225

Woodley SM; Battle PD; Gale JD; Catlow CRA

The prediction of inorganic crystal structures
using a genetic algorithm and energy minimisation

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 1999, Vol
1, Iss 10, pp 2535-2542

Harris KDM; Johnston RL; Kariuki BM; Tremayne
M

A genetic algorithm for crystal structure solution
from powder diffraction data

JOURNAL OF CHEMICAL RESEARCH-S 1998, Iss 7, pp
390-+

Putz H; Schon JC; Jansen M

Combined method for ab initio structure solution
from powder diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 864-870

Wessels T; Baerlocher C; McCusker LB

Single-crystal-like diffraction data from polycrystalline
materials

SCIENCE 1999, Vol 284, Iss 5413, pp 477-479

Hammond RB; Roberts KJ; Smith EDL; Docherty R

Application of a computational systematic search
strategy to study polymorphism in phenazine and perylene

JOURNAL OF PHYSICAL CHEMISTRY B 1999, Vol 103,
Iss 37, pp 7762-7770

Kariuki BM; Belmonte SA; McMahon MI; Johnston
RL; Harris KDM; Nelmes RJ

A new approach for indexing powder diffraction
data based on whole-profile fitting and global optimization using a genetic
algorithm

JOURNAL OF SYNCHROTRON RADIATION 1999, Vol 6,
pp 87-92

Reardon BJ

Optimization of densification modelling parameters
of beryllium powder using a fuzzy logic based multiobjective genetic algorithm

MODELLING AND SIMULATION IN MATERIALS SCIENCE
AND ENGINEERING 1998,

Vol 6, Iss 6, pp 735-746

Csoka T; David WIF; Shankland K

Crystal structure determination from powder diffraction
data by the application of a genetic algorithm

EPDIC 5, PTS 1 AND 2 1998, Vol 278-2, pp 294-299

Paszkowicz W

Application of the smooth genetic algorithm for
indexing powder patterns - Tests for the orthorhombic system

EUROPEAN POWDER DIFFRACTION: EPDIC IV, PTS 1
AND 2 1996, Vol 228, pp 19-24

De Gelder R; Wehrens R; Hageman JA

A generalized expression for the similarity of
spectra: Application to powder diffraction pattern classification

JOURNAL OF COMPUTATIONAL CHEMISTRY 2001, Vol
22, Iss 3, pp 273-289

Bond AD; Feeder N; Teat SJ; Jones W

The solid-state structure of 3-hydroxy-4-methyl-2(3H)-thiazolethione:
Prediction and measurement

TETRAHEDRON 2000, Vol 56, Iss 36, pp 6617-6624

Turner GW; Tedesco E; Harris KDM; Johnston RL;
Kariuki BM

Implementation of Lamarckian concepts in a Genetic
Algorithm for structure solution from powder diffraction data

CHEMICAL PHYSICS LETTERS 2000, Vol 321, Iss 3-4,
pp 183-190

Reardon BJ; Bingert SR

Inversion of tantalum micromechanical powder
consolidation and sintering models using Bayesian inference and genetic
algorithms

ACTA MATERIALIA 2000, Vol 48, Iss 3, pp 647-658

Reardon BJ

Inversion of micromechanical powder consolidation
and sintering models using Bayesian inference and genetic algorithms

MODELLING AND SIMULATION IN MATERIALS SCIENCE
AND ENGINEERING 1999, Vol 7, Iss 6, pp 1061-1081

Harris KDM; Johnston RL; Kariuki BM

An evolving technique for powder structure solution
- fundamentals and applications of the genetic algorithm

ANALES DE QUIMICA-INTERNATIONAL EDITION 1998,
Vol 94, Iss 6, pp 410-416

Kariuki BM; Johnston RL; Harris KDM; Psallidas
K; Ahn S; Serrano-Gonzalez H

Application of a Genetic Algorithm in structure
determination from powder diffraction data

MATCH-COMMUNICATIONS IN MATHEMATICAL AND IN COMPUTER
CHEMISTRY 1998, Iss 38, pp 123-135

Yan JQ; Zhang PX; Wu WQ; Shan SG; Sui ZT

Artificial neural networks and genetic algorithm
used to optimize process parameters of reaction-sintered ZrO2-SiC(p) ceramics

JOURNAL OF INORGANIC MATERIALS 1998, Vol 13,
Iss 6, pp 937-940

Knorr K; Madler F

The application of evolution strategies to disordered
structures

JOURNAL OF APPLIED CRYSTALLOGRAPHY 1999, Vol
32, pp 902-910

Weber-T; Burgi-HB

Determination and refinement of disordered crystal
structures using evolutionary algorithms in combination with Monte Carlo
methods

ACTA-CRYSTALLOGRAPHICA-SECTION-A. NOV 2002; 58
Part 6 : 526-540

HABERSHON-Scott; HARRIS-Kenneth-D-M; JOHNSTON-Roy-L;
TURNER-Giles-W; JOHNSTON-Jennifer-M

Gaining insights into the evolutionary behaviour
in genetic algorithm calculations, with applications in structure solution
from powder diffraction data

Chemical-physics-letters. 2002; 353 (3-4) : 185-194

A general strategy is introduced for analysing
the evolutionary events that occur during a genetic algorithm calculation,
and the application of this approach is illustrated for the specific case
of understanding the evolutionary trajectory leading to the correct structure
solution in structure determination from powder diffraction data.

Chernyshev VV; Schenk H

A grid search procedure of positioning a known
molecule in an unknown crystal structure with the use of powder diffraction
data

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 1998, Vol 213,
Iss 1, pp 1-3

Mora AJ; Fitch AN

The low-temperature crystal structure of RS-camphor

JOURNAL OF SOLID STATE CHEMISTRY 1997, Vol 134,
Iss 1, pp 211-214

FREEMAN CM; NEWSAM JM; LEVINE SM; CATLOW CRA

INORGANIC CRYSTAL-STRUCTURE PREDICTION USING
SIMPLIFIED POTENTIALS AND EXPERIMENTAL UNIT CELLS - APPLICATION TO THE
POLYMORPHS OF TITANIUM-DIOXIDE

JOURNAL OF MATERIALS CHEMISTRY 1993, Vol 3, Iss
5, pp 531-535

Buttar D; Charlton MH; Docherty R; Starbuck J

Theoretical investigations of conformational
aspects of polymorphism. Part 1: O-acetamidobenzamide

JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS
2 1998, Iss 4, pp 763-772

van Eijck BP; Kroon J

UPACK program package for crystal structure prediction:
Force fields and crystal structure generation for small carbohydrate molecules

JOURNAL OF COMPUTATIONAL CHEMISTRY 1999, Vol
20, Iss 8, pp 799-812

Filippini G; Gavezzotti A; Novoa JJ

Modelling the crystal structure of the 2-hydronitronylnitroxide
radical (HNN): observed and computer-generated polymorphs

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
1999, Vol 55, pp

543-553

Breu J; Domel H; Norrby PO

Chiral recognition among trisdiimine-metal complexes,
7 - Racemic compound formation versus conglomerate formation with [M(bpy)(3)](PF6)(2)
(M = Ni, Zn, Ru); Lattice energy minimisations and implications for structure
prediction

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2000,
Iss 11, pp 2409-2419

Lommerse JPM; Motherwell WDS; Ammon HL; Dunitz
JD; Gavezzotti A; Hofmann DWM; Leusen FJJ; Mooij WTM; Price SL; Schweizer
B; Schmidt MU; van Eijck BP; Verwer P; Williams DE

A test of crystal structure prediction of small
organic molecules

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
2000, Vol 56, pp 697-714

van Eijck BP; Kroon J

Structure predictions allowing more than one
molecule in the asymmetric unit

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
2000, Vol 56, pp 535-542

Newsam JM; Freeman CM; Leusen FJJ

Crystal structure solution and prediction via
global and local optimization

CURRENT OPINION IN SOLID STATE & MATERIALS
SCIENCE 1999, Vol 4, Iss 6, pp

515-528

Bond AD; Feeder N; Teat SJ; Jones W

The solid-state structure of 3-hydroxy-4-methyl-2(3H)-thiazolethione:
Prediction and measurement

TETRAHEDRON 2000, Vol 56, Iss 36, pp 6617-6624

Smrcok L; Durik M

On reliability of R-wp in structure modelling

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 2000, Vol 215,
Iss 7, pp 384-385

Chin DN; Palmore GTR; Whitesides GM

Predicting crystalline packing arrangements of
molecules that form hydrogen-bonded tapes

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 1999,
Vol 121, Iss 10, pp 2115-2122

A. Gavezzotti & G. Filippini,

Computer prediction of organic crystal structures
using partial X-ray diffraction data,

J. Amer. Chem. Soc. 118 (1996) 7153-7157.

Gavezzotti-A

Structure and intermolecular potentials in molecular
crystals

MODELLING-AND-SIMULATION-IN-MATERIALS-SCIENCE-AND-ENGINEERING.
MAY 2002; 10 (3) : R1-R29

Polymorphism, phase transitions and the attempts
at crystal structure prediction are examined, together with models for
the reproduction and possible prediction of crystal morphology. Simulations
of crystal growth and nucleation, also extremely important for prediction
and control of organic crystal structures, are discussed.

Mellot-Draznieks-C; Girard-S; Ferey-G; Schon-JC;
Cancarevic-Z; Jansen-M

Computational design and prediction of interesting
not-yet-synthesized structures of inorganic materials by using building
unit concepts

CHEMISTRY-A-EUROPEAN-JOURNAL. SEP 16 2002; 8
(18) : 4103-4113

A. D. Bond and W. Jones

Structure prediction as a tool for solution of
the crystal structures of metallo-organic complexes using powder X-ray
diffraction data

Acta Cryst. (2002). B58, 233-243

Schon-JC; Jansen-M

Determination, prediction, and understanding
of structures, using the energy landscapes of chemical systems - Part I

ZEITSCHRIFT-FUR-KRISTALLOGRAPHIE. 216 (2001)
: 307-325

Schon-JC; Jansen-M

Determination, prediction, and understanding
of structures, using the energy landscapes of chemical systems - Part III

ZEITSCHRIFT-FUR-KRISTALLOGRAPHIE. 216 (2001)
361-383

These include structure prediction of extended
and molecular crystals, structure prediction and folding of proteins, structure
analysis of zeolites, and structure determination of crystals from powder
diffraction data.

Potter BS. Palmer RA. Withnall R. Chowdhry BZ.
Price SL.

Aza analogues of nucleic acid bases: experimental
determination and computational prediction of the crystal structure of
anhydrous 5-azauracil

J. Mol. Struct. 486(Special Issue SI):349-361,
1999.

T.S. Bush, C.R.A. Catlow and P.D. Battle,

Evolutionary programming techniques for predicting
inorganic crystal structures

J. Mater. Chem. 5 (1995) 1269-1272.

Molecule packing prediction, blind tests, etc

Day, GM Motherwell, WDS

An experiment in crystal structure prediction by popular vote

CRYSTAL GROWTH & DESIGN 6, 2006, 1985-1990.

The ability to identify the crystal structures of small molecules by

visual inspection, given a list of computer-generated
low-energy

possibilities, has been tested in an experiment conducted
at an

international crystallographic conference. The surprising
result of the

test was that the experimentally observed crystal structures
were the

least popular of five choices for the two molecules included
in the

test, casting doubt on the reliability of crystallographic
intuition as

a complement to computational methods in crystal structure
prediction.

Day, GM Motherwell, WDS Ammon, HL
Boerrigter, SXM Della Valle, RG

Venuti, E Dzyabchenko, A Dunitz,
JD Schweizer, B van Eijck, BP

Erk, P Facelli, JC Bazterra, VE
Ferraro, MB Hofmann, DWM

Leusen, FJJ Liang, C Pantelides,
CC Karamertzanis, PG

Price, SL Lewis, TC Nowell, H
Torrisi, A Scheraga, HA

Arnautova, YA Schmidt, MU Verwer,
P

A third blind test of crystal structure prediction

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 61, 2005, 511-527.

Following the interest generated by two previous blind tests of crystal

structure prediction (CSP1999 and CSP2001), a third such
collaborative

project (CSP2004) was hosted by the Cambridge Crystallographic
Data

Centre. A range of methodologies used in searching for
and ranking the

likelihood of predicted crystal structures is represented
amongst the

18 participating research groups, although most are based
on the global

minimization of the lattice energy. Initially the participants
were

given molecular diagrams of three molecules and asked
to submit three

predictions for the most likely crystal structure of each.
Unlike

earlier blind tests, no restriction was placed on the
possible space

group of the target crystal structures. Furthermore, Z'
= 2 structures

were allowed. Part-way through the test, a partial structure
report was

discovered for one of the molecules, which could no longer
be

considered a blind test. Hence, a second molecule from
the same

category (small, rigid with common atom types) was offered
to the

participants as a replacement. Success rates within the
three submitted

predictions were lower than in the previous tests - there
was only one

successful prediction for any of the three 'blind' molecules.
For the

'simplest' rigid molecule, this lack of success is partly
due to the

observed structure crystallizing with two molecules in
the asymmetric

unit. As in the 2001 blind test, there was no success
in predicting the

structure of the flexible molecule. The results highlight
the necessity

for better energy models, capable of simultaneously describing

conformational and packing energies with high accuracy.
There is also a

need for improvements in search procedures for crystals
with more than

one independent molecule, as well as for molecules with
conformational

flexibility. These are necessary requirements for the
prediction of

possible thermodynamically favoured polymorphs. Which
of these are

actually realised is also influenced by as yet insufficiently

understood processes of nucleation and crystal growth.

Day, GM Motherwell, WDS Jones, W

Beyond the isotropic atom model in crystal structure prediction of

rigid molecules: Atomic multipoles versus point charges

CRYSTAL GROWTH & DESIGN 5, 2005, 1023-1033.

The lattice energies of predicted and known crystal structures for
50

small organic molecules with constrained (rigid) geometries
have been

calculated with a model potential whose electrostatic
component is

described by atom-centered multipoles. In comparison to
previous

predictions using atomic point charge electrostatics,
there are

important improvements in the reliability of lattice energy

minimization for the prediction of crystal structures.
Half of the

experimentally observed crystal structures are found either
to be the

global minimum energy structure or to have calculated
lattice energies

within 0.5 kJ/mol (0.1 kcal/mol) of the global minimum.
Furthermore, in

69% of cases, there are five or fewer unobserved structures
with

lattice energies calculated to be lower than that of the
observed

structure. The results are promising for the advancement
of global

lattice energy minimization for the ab initio prediction
of crystal

structures and confirm the utility of representing electrostatic

contributions to the energy with atom-centered multipoles.

Day, GM Chisholm, J Shan, N Motherwell,
WDS Jones, W

Assessment of lattice energy minimization for the prediction of

molecular organic crystal structures

CRYSTAL GROWTH & DESIGN 4, 2004, 1327-1340.

Lattice energy searches for theoretical low-energy crystal forms are

presented for 50 small organic molecules, and we compare
the

experimentally observed crystal forms to these lists of
hypothetical

polymorphs. For each known crystal, the relative stability
is

calculated with respect to the global minimum energy structure,
and we

determine the number of unobserved structures lower in
energy than the

experimental form. The distributions of these relative
energies and

their rankings in the predicted lists are used to determine
the

efficacy of lattice energy minimization in crystal structure

prediction. Although a simple form for the interaction
energies has

been used, the calculations produce almost a third of
the known

crystals as the global minimum in energy, and approximately
a half of

the known structures are within 1 kJ/mol of the global
minimum.

Molecules with no hydrogen-bonding capacity are most likely
to be found

close to the global minimum in lattice energy, while increasing
the

number of possible hydrogen-bond donor-acceptor combinations
leads to

less reliable predictions.

Pidcock, E Motherwell, WDS

A novel description of the crystal packing of molecules

CRYSTAL GROWTH & DESIGN 4, 2004, 611-620.

The question of why molecules pack to form particular crystal

structures is occupying many researchers throughout the
scientific

community. Much emphasis has been placed on the study
of intermolecular

interactions and the search for "structure-directing"
motifs. However,

examination of experimental crystal structures contained
within the

Cambridge Structural Database has led us to propose a
new, conceptually

simple model of crystal packing that describes the arrangements

molecules adopt in unit cells. The model was inspired
by consideration

of arrangements of boxes (with three unequal dimensions)
stacked with

faces touching and edges aligned. For a fixed number of
boxes, there

are only a limited number of arrangements possible, and
these

arrangements, or packing patterns, are of the same volume
but different

surface area. Applied to crystal structures, the model
describes unit

cells in terms of multiples (pattern coefficients) of
molecular

dimensions. The different packing patterns are not populated
equally by

experimental crystal structures, and it is found that
the most

populated packing patterns are those that are characterized
by low

surface area. Correlations between broadly defined molecular
shapes and

packing patterns have been observed which indicate that
molecular

aggregation is a useful method for moderating awkward
(high surface

area for volume) molecular shapes. A limited number of
crystal

structure prediction trials were performed with the reduced
search

space afforded by estimated unit cell dimensions (from
molecular

dimensions), and an increase in success rate was observed.

Motherwell, WDS Ammon, HL Dunitz, JD
Dzyabchenko, A Erk, P

Gavezzotti, A Hofmann, DWM Leusen,
FJJ Lommerse, JPM

Mooij, WTM Price, SL Scheraga,
H Schweizer, B Schmidt, MU

van Eijck, BP Verwer, P Williams,
DE

Crystal structure prediction of small organic molecules: a second blind

test

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 58, 2002, 647-661.

The first collaborative workshop on crystal structure prediction

(CSP1999) has been followed by a second workshop (CSP2001)
held at the

Cambridge Crystallographic Data Centre. The 17 participants
were given

only the chemical diagram for three organic molecules
and were invited

to test their prediction programs within a range of named
common space

groups. Several different computer programs were used,
using the

methodology wherein a molecular model is used to construct
theoretical

crystal structures in given space groups, and prediction
is usually

based on the minimum calculated lattice energy. A maximum
of three

predictions were allowed per molecule. The results showed
two correct

predictions for the first molecule, four for the second
molecule and

none for the third molecule (which had torsional flexibility).
The

correct structure was often present in the sorted low-energy
lists from

the participants but at a ranking position greater than
three. The use

of non-indexed powder diffraction data was investigated
in a secondary

test, after completion of the ab initio submissions. Although
no one

method can be said to be completely reliable, this workshop
gives an

objective measure of the success and failure of current
methodologies.

Motherwell, WDS

Crystal structure prediction and the Cambridge Structural Database

MOLECULAR CRYSTALS AND LIQUID CRYSTALS 356, 2001, 559-567.

A computer program has been written to attempt prediction of likely

polymorphs of small organic molecules, using a genetic
algorithm. The

cost function used is based not on energy but the intermolecular
atom

pair distances as seen in the Cambridge database, for
selected similar

molecules to the target. Some successful results are described,
showing

possible applications to molecules not easily treated
with empirical

energy potentials.

Lommerse, JPM Motherwell, WDS Ammon, HL
Dunitz, JD Gavezzotti, A

Hofmann, DWM Leusen, FJJ Mooij,
WTM Price, SL Schweizer, B

Schmidt, MU van Eijck, BP Verwer,
P Williams, DE

A test of crystal structure prediction of small organic molecules

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 56, 2000, 697-714.

A collaborative workshop was held in May 1999 at the Cambridge

Crystallographic Data Centre to test how well currently
available

methods of crystal structure prediction perform when given
only the

atomic connectivity for an organic compound. A blind test
was conducted

on a selection of four compounds and a wide range of methodologies

representing the principal computer programs currently
available were

used. There were 11 participants who were allowed to propose
at most

three structures for each compound. No program gave consistently

reliable results. However, seven proposed structures were
close to an

experimental one and were classified as 'correct'. One
compound

occurred in two polymorphs, but only one form was predicted
correctly

among the calculated structures. The basic problem with
lattice energy

based methods of crystal structure prediction is that
many structures

are found within a few kJ mol(-1) of the global minimum.
The fine

detail of the force-field methodology and parametrization
influences

the energy ranking within each method. Nevertheless, present
methods

may be useful in providing a set of structures as possible
polymorphs

for a given molecular structure.

Prediction

Cancarevic, Z Schon, JC Jansen, M

Alkali metal carbonates at high pressure

ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 632, 2006, 1437-1448.

The possible existence of crystalline alkali metal carbonates as

high-pressure modifications in the system M2CO3, where
M = Li, Na, K,

Rb, and Cs are investigated. The results agree well with
the

experimental observations at standard pressure, and several
new

modifications are proposed that should be thermodynamically
stable at

high and effective negative pressures.

Le Bail, A Calvayrac, F

Hypothetical AlF3 crystal structures

JOURNAL OF SOLID STATE CHEMISTRY 179, 2006, 3159-3166.

Applying a structure prediction computer programme (GRINSP =

Geometrically Restrained INorganic Structure Prediction),
the

occurrence of 6-connected 3D networks was investigated,
through AlF6

octahedra exclusive corner sharing. The five known AlF3
varieties were

reproduced (alpha-, beta-, eta-, K- and tau-AlF3) and
seven

hypothetical models were predicted. Among these still
to be synthesized

AlF3 phases, one can recognize two known structure types
(TICa2Ta5O15,

Ba4CoTa10O30) and some easy to imagine intergrowths; however,
a few

others are completely unexpected, though simple. A comparison
of the ab

initio total energies of all the structures is provided,
leading to the

conclusion that the virtual models could well be viable.

Florence, AJ Leech, CK Shankland, N
Shankland, K Johnston, A

Control and prediction of packing motifs: a rare occurrence of

carbamazepine in a catemeric configuration

CRYSTENGCOMM 8, 2006, 746-747.

A predicted orthorhombic crystal structure of carbamazepine is

isostructural with an experimentally determined dihydrocarbamazepine

crystal structure, providing a rationale for synthesising
a novel 1 : 1

solid solution that has carbamazepine in a rare catemeric
configuration.

Mellot-Draznieks, C Ferey, G

Assembling molecular species into 3D frameworks: Computational design

and structure solution of hybrid materials

PROGRESS IN SOLID STATE CHEMISTRY 33, 2005, 187-197.

We present here the computational prediction of hybrid

organic-inorganic extended lattices. The production of
candidate

crystal structures is successfully performed by direct-space
assembly

of building-units using the AASBU (Automated Assembly
of Secondary

Building Units) method, mixing independent organic and
inorganic units.

Hybrid candidates that are compatible with the imposed
metal:organic

ratio are generated with their cell parameters, space
group, atomic

positions, along with their simulated diffraction pattern.
Since no

explicit limit regarding the nature, number, and size
of the inorganic

and organic units, or hybrid building-block is involved,
the method

offers boundless potential for exploring hybrid frameworks
in terms of

the topological diversity. The most appealing development
arises from

the computer-assisted design of hybrid frameworks. Indeed,
in a

significant number of systems, it is well-known that controlled

synthesis conditions can promote the occurrence of specific

building-units, which serve to "propagate" the infinite
crystal

structure. We believe that the computational approach
presented herein

is valuable to create virtual libraries of viable hybrid
polymorphs. We

further show how it has proven to be, for the first time
in the realm

of hybrids, a tangible route towards structure solution
in direct

space, exemplified here with the computational structure
determination

of two complex hybrid structures, MIL-100 and MIL-101.
This challenging

area is of special interest when high quality diffraction
data are not

available or when very large cell sizes are involved.
The development

of a structural model in direct space, starting with minimal
knowledge

such as the metal:organic ratio, is shown here to be possible.
With

such a method in hand, formerly intractable structural
problems when

using methods based on conventional reciprocal space become
feasible in

direct space.

Mellot-Draznieks, C Ferey, G

Simulations of inorganic crystal structures recent advances in

structure elucidation

CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE 7, 2003, 13-19.

The aim of this paper is to show some recent developments of simulation

approaches in the structure elucidation of inorganic crystalline

compounds, highlighting at each step their role either
as a

complementary technique or as a tool to anticipate structure/properties

relationships or even to imagine new inorganic architectures.
Specific

examples are taken in the area of zeolites to illustrate
the use of

energy minimizations and (N, V, T) Monte Carlo techniques
as a

complement to experimental diffraction approaches, typically
for the

disordered placement of extra-framework species (cations,
water

molecules). In the still extending area of the synthesis
of templated

open-framework inorganic structures, we show that lattice
energy

minimizations may possibly be used to estimate or even
anticipate the

structures and energetics of the related template-free
structures. A

third section tackles the development of more sophisticated
methods for

the computational design of not-yet-synthesized structures
using

building block concepts.

Le Bail, A

Inorganic structure prediction with GRINSP

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 389-395.

A new computer program is described, GRINSP ( geometrically restrained

inorganic structure prediction), which allows the exploration
of the

possibilities of occurrence of 3-, 4-, 5- and 6-connected

three-dimensional networks. Hypothetical ( as well as
known structure)

models for binary compounds are produced with exclusive
connection of

polyhedra by corners, such as [MX3] triangles in M2X3
formulation,

[MX4] tetrahedra in MX2 ( zeolites or dense SiO2 polymorphs),
[MX5]

polyhedra in M2X5, and finally [MX6] octahedra in MX3
polymorphs.

Moreover, hypothetical ternary compounds are built up
by combinations

of either two different polyhedra or two different radii
for two

different cations adopting the same coordination. The
cost function is

based on the agreement of the model interatomic distances
with ideal

distances provided by the user. The Monte Carlo algorithm
first finds

structure candidates selected after the verification of
the expected

geometry, and then optimizes the cell parameters and the
atomic

coordinates. A satellite software ( GRINS) uses the predicted
models

and produces the characteristics of isostructural compounds
which would

be obtained by cationic substitutions. A huge list of
CIF files of

hypothetical boron oxide polymorphs ( including nanotubes),
zeolites,

aluminium and 3d-element fluorides, fluoroaluminates,
borosilicates,

titanosilicates, gallophosphates etc., is freely available
at the PCOD

( Predicted Crystallography Open Database).

Schon, JC Cancarevic, Z Jansen, M

Structure prediction of high-pressure phases for alkali metal sulfides

JOURNAL OF CHEMICAL PHYSICS 121, 2004, 2289-2304.

For a given chemical system we present a systematic approach to predict

structures, which may exist at high pressure, by investigating
the

global enthalpy landscape. We combine global optimizations,
based on

empirical potential energy functions, and local optimizations
(volume,

cell shape, and atomic positions) on both Hartree-Fock
and density

functional theory level. We predict the existence of high-pressure

phases for the alkali metal sulfides of the composition
M2S (M=Li, Na,

K, Rb, Cs), together with the transition pressures among
these phases.

Gibbons, PC Hennig, RG Huett, VT
Kelton, KF

Ti-Zr-Ni and Ti-Hf-Ni quasicrystals and approximants as hydrogen

storage alloys

JOURNAL OF NON-CRYSTALLINE SOLIDS 334, 2004, 461-465.

X-ray and neutron powder diffraction data previously collected from
the

Ti-Zr-Ni quasicrystal have been analyzed. The data were
modeled by an

8/5 rational approximant (RA) that was constructed using
the known

structure of the 1/1 RA and then refined. Ab initio total
energy

calculations were made for small structures with between
81 and 123

atoms, in which atomic positions were allowed to vary
while minimizing

the energy. The final structure is in good agreement with
that obtained

from the scattering data. Interstitial sites in which
H is stable in

the 1/1 model, and the H binding energies, were identified.
An

excellent fit to existing pressure-composition isotherms
was obtained,

but those data cannot be inverted to obtain experimental
site binding

energies. At 250 degreesC the Ti-Hf-Ni alloy can be loaded
with H

without the formation of any detectable crystal hydride
phase, which is

always found in similarly loaded Ti-Zr-Ni alloys.

Cancarevic, ZP Schon, JC Jansen, M

Structure prediction of solids: Heuristic algorithms for local

optimization on Hartree-Fock level

PROGRESS IN ADVANCED MATERIALS AND PROCESSES

MATERIALS SCIENCE FORUM 453-454, 2004, 71-76.

In recent years, the prediction of new not-yet-synthesized solid phases

and the theoretical determination of the structure of
already

synthesized compounds from cell information only have
become of

increasing importance. For example, it would be of great
advantage in

the identification of newly generated phases in high-pressure

experiments, if one could supplement the experimental
results with

theoretical studies on the same system.

The prediction of high pressure phases of a chemical system
is realized

as a two-step process: identification of structure candidates
via

global exploration of the energy landscapes over a range
of different

pressures followed by a local optimization of the candidates
on

ab-initio level. From the completed E(V)-curves, one could
then

calculate the stable phase at a given pressure and the
transition

pressures among the phases.

In this work we will focus on the local optimization of
the cell

parameters and relative atom positions on the Hartree-Fock
level. We

present a heuristic algorithm for the full local optimization
of all

structural parameters and show, taking Na2S as an example,
how this

leads to a significant improvement in e.g. the agreement
between

computed and measured transition pressures.

Nagayoshi, K Ikeda, T Kitaura, K
Nagase, S

Computational procedure of lattice energy using the ab initio MO method

JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2, 2003, 233-234.

Recently, we have proposed a computational procedure for calculations

of lattice energies of molecular crystals using the ab
initio MO

method. This procedure does not use potential functions
and is

applicable to a variety of molecular crystals. The procedure
has been

successfully applied to calculation of packing structure
of electron

donor-acceptor complex, H3N-BF3, and hydrogen bonding
crystal, CH3OH.

In this work, we present a full account of the computational
procedure.

This method is applied to the packing structure calculations
of

hydrocarbon crystals, C2H2, C2H4 and C6H6. The lattice
parameters

optimized at the MP2/6-311++G** level are in good agreement
with the

experimental values. The basis set dependence of the lattice
constants

is also discussed for several crystals.

Kratochvil, B Husak, M Jegorov, A

Polymorphism and solvatomorphism of solid substances in pharmacy

CHEMICKE LISTY 96, 2002, 330-335.

The ability of a particular substance to exist in several different

crystal forms (unsolvated or solvated) is called polymorphism
or

solvatomorphism. These phenomena are frequently observed
in solid

pharmaceuticals. Polymorphs and solvatomorphs of a compoud
differ in

their physical and biological properties (crystal shape,
hardness,

melting point, solubility, pharmacokinetics, bioavailability,
etc.).

This influences commercial drug formulations and their
therapeutical

effect, The exact theoretical prediction of all polymorphs
and

solvatomorphs is not yet possible. The most frequently
used analytical

method of detection and characterization of polymorphic
and

solvatomorphic forms is X-ray diffraction (single-crystal
structure

analysis and collection of powder patterns), Producers
of original

pharmaceuticals endeavour to patent all crystal forms
of the developed

active substance, while generic producers search for new
polymorphs

(solvatomorphs) or technologies. Clearly this can cause
lawsuits.

Van Droogenbroeck, J Swerts, B Schafer, L
Van Alsenoy, C

Solids modeled by ab initio crystal field methods, Part 22: The Fock

matrix transformed supermolecule model and the structure
determination

of D-erythronic acid-3,4-carbonate

JOURNAL OF COMPUTATIONAL CHEMISTRY 25, 2004, 2065-2072.

To eliminate the cutoff effects in the supermolecule model (SM), the

Fock matrix transformed supermolecule model (FTSM) is
developed. In

this model a cyclization of the cluster is performed by
means of

transformations of elements of the Fock matrix, thereby
restoring the

translational symmetry. Besides this fundamental enhancement,

significant CPU time savings are realized because, in
this new

procedure, not all Fock matrix elements need to be calculated.
The

method is applied in a study of the structure of D-erythronic

acid-3,4-carbonate in the crystal phase, where the new
model is

compared to the supermolecule model as well as the XRD
experiment. The

results are found to be in good agreement with experimental
data.

Hofmann, DWM Apostolakis, J

Crystal structure prediction by data mining

JOURNAL OF MOLECULAR STRUCTURE 647, 2003, 17-39.

The ever increasing number of experimentally determined crystal.

structures allows for the use of data mining methods to,
address

crystallographic questions. Here we study the application
of data

mining for predicting the arrangement of molecules in
unit cells of

unknown dimensions (crystal structure prediction) as well
as in unit

cells of predetermined dimensions (fractional coordinate
prediction).

In this work, data mining is used to derive an atom-pair
potential,

which is then compared-to known force fields. It is shown
that the

potential is-physically reasonable when the data are sufficient
in

quality and quantity. For validation the energy function
is applied to

the problems of crystal structure prediction and fractional
coordinate

prediction. In both cases a large number of structures-was
generated

and the structures were ranked according to their energies.
Structure

prediction was considered successful if a structure similar
to the

experimentally observed one was ranked highest.

For crystal structure prediction the energy function is
tested on

an-independent set of crystal, structures taken from the
P1 and P (1)

over bar space groups. We show that approximately 76%
of the 218

molecules tested-in, space group P1 are predicted correctly.
For the

more complex space group P (1) over bar the success rate
is 24%.

If the powder diffraction can be indexed, the problem
simplifies to

fractional coordinate prediction. With the assumption
of known cell

parameters the structure has been resolved in 92% of the
test-cases for

P1 and 29% for P1.

Tedesco, E Giron, D Pfeffer, S

Crystal structure elucidation and morphology study of pharmaceuticals

in development

CRYSTENGCOMM 2002, 393-400.

The structural characterization of drug substances by X- ray

diffraction plays a central role during the development
of

pharmaceuticals. While powder diffraction is usually employed
for the

identification of solid phases, the single crystal technique
yields

detailed structural information, which is needed for purity
control,

understanding of polymorphism or pseudo-polymorphic behavior,

physico-chemical property elucidation and morphology characterization.

The structure determination of three active ingredients
is discussed in

this context. In the first case, we have solved the structure
directly

from high- resolution powder X-ray data, using the `direct-space'

methodology. The polymorphic behavior of the second substance
has been

rationalized by analyzing the intermolecular interactions
and packing

motifs of the two modifications in the solid state. For
the third

compound, we have predicted the morphology from the knowledge
of its

crystal structure. Solvent mixtures have been used to
control the

external crystal habit, based upon a detailed analysis
of chemical

groups emerging from the cleaved crystal surfaces of the
calculated

morphology.

Mellot-Draznieks, C Girard, S Ferey, G
Schon, JC Cancarevic, Z Jansen, M

Computational design and prediction of interesting not-yet-synthesized

structures of inorganic materials by using building unit
concepts

CHEMISTRY-A EUROPEAN JOURNAL 8, 2002, 4103-4113.

The computational design of new and interesting inorganic materials
is

still an ongoing challenge. The motivation of these efforts
is to aid

the often difficult task of crystal structure determination,
to

rationalize different but related structure types, or
to help limit the

domain of structures that are possible in a given system.
Over the past

decade, simulation methods have continuously evolved towards
the

prediction of new structures using minimal input information
in terms

of symmetry, cell parameters, or chemical composition.
So far, this

task of identifying candidate structures through an analysis
of the

energy landscape of chemical systems has been particularly
successful

for predominantly ionic systems with relatively small
numbers of atoms

or ions in the simulation cell. After an introductory
section, the

second section of this work presents the historical developments
of

such simulation methods in this area. The following sections
of the

work are dedicated to the introduction of the building
unit concept in

simulation methods: we present simulation approaches to
structure

prediction employing both primary (aggregate of atoms)
and secondary

(aggregate of coordination polyhedra) building units.
While structure

prediction with primary units is a straightforward extension
of

established approaches, the AASBU method (automated asssembly
of

secondary building units) focusses on the topology of
network-based

structures. This method explores the possible ways to
assemble

predefined inorganic building units in three-dimensional
space, opening

the way to the manipulation of very large building units
(up to 84

atoms in this work). As illustrative examples we present
the prediction

of candidate structures for Li4CO4, the identification
of topological

relationships within a family of metalphosphates, ULM-n
and MIL-n, and

finally the generation of new topologies by using predefined
large

building units such as a sodalite or a double-four-ring
cage, for the

prediction of new and interesting zeolite-type structures.

Bond, AD Jones, W

Structure prediction as a tool for solution of the crystal structures

of metallo-organic complexes using powder X-ray diffraction
data

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 58, 2002, 233-243.

A simulated-annealing direct-space approach has been applied to predict

the crystal structures of a series of metallo-organic
complexes

containing Zn, Cu and Ni. The prediction methodology generates
a set of

energetically reasonable crystal structures among which
the actual

structure is present, but it is not always possible to
specify

unambiguously the known crystal structure solely on the
basis of

energy. In each case, however, the ambiguity may be resolved
by

recourse to laboratory powder X-ray diffraction (PXRD)
data. In this

manner, structure prediction is shown to be a powerful
tool for

structure solution using PXRD data, with the additional
advantage that

indexing of the PXRD profile is not required at the outset.

2001

Schon, JC Jansen, M

Determination, prediction, and understanding of structures, using the

energy landscapes of chemical systems - Part III

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 216, 2001, 361-383.

In the past decade, new theoretical approaches have been developed
to

determine, predict and understand the structure of chemical
compounds.

The central element of these methods has been the investigation
of the

energy landscape of chemical systems. Applications range
from extended

crystalline and amorphous compounds over clusters and
molecular

crystals to proteins. In this review, we are going to
give an

introduction to energy landscapes and methods for their
investigation,

together with a number of examples. These include structure
prediction

of extended and molecular crystals, structure prediction
and folding of

proteins, structure analysis of zeolites, and structure
determination

of crystals from powder diffraction data.

Instruments

Ferreira, FF Granado, E Carvalho, W
Kycia, SW Bruno, D Droppa, R

X-ray powder diffraction beamline at D10B of LNLS: application to the

Ba2FeReO6 double perovskite

JOURNAL OF SYNCHROTRON RADIATION 13, 2006, 46-53.

A new beamline, fully dedicated to X-ray powder diffraction (XPD)

measurements, has been installed after the exit port B
of the bending

magnet D10 at the Brazilian Synchrotron Light Laboratory
(LNLS) and

commissioned. The technical characteristics of the beamline
are

described and some performance indicators are listed,
such as the

incoming photon flux and the angular/energy resolutions
obtainable

under typical experimental conditions. The results of
a Rietveld

refinement for a standard sample of Y2O3 using high-resolution
data are

shown. The refined parameters match those found in the
literature,

within experimental error. High-resolution XPD measurements
on

Ba2FeReO6 demonstrate a slight departure from the ideal
cubic

double-perovskite structure at low temperatures, not detected
by

previous powder diffraction experiments. The onset of
the structural

transition coincides with the ferrimagnetic ordering temperature,

T(c)similar or equal to 315 K. Subtle structural features,
such as

those reported here for Ba2FeReO6, as well as the determination
and/or

refinement of complex crystal structures in polycrystalline
samples are

ideal candidate problems to be investigated on this beamline.

Knapp, M Baehtz, C Ehrenberg, H
Fuess, H

The synchrotron powder diffractometer at beamline B2 at HASYLAB/DESY:

status and capabilities

JOURNAL OF SYNCHROTRON RADIATION 11, 2004, 328-334.

The synchrotron powder diffraction beamline B2 at HASYLAB/DESY is

described. The beamline is capable of high-resolution
powder

diffraction as well as time-resolved studies and offers
several

sophisticated ancillary equipments for special applications.
A newly

developed image-plate system allows for kinetic studies
with good

resolution in the minutes range. Numerous sample environments
allow for

various standard applications including structure solution,
kinetic

studies and in situ observations under flexible and well
defined

conditions. Representative examples are shown for these
setups, which

are also supported for experiments of external users.

Fitch, AN

The high resolution powder diffraction beam line at ESRF

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND

TECHNOLOGY 109, 2004, 133-142.

The optical design and performance of the high-resolution powder

diffraction beam line BM16 at ESRF are discussed and illustrated.
Some

recent studies carried out on BM16 are described, including
crystal

structure solution and refinement, anomalous scattering,
in situ

measurements, residual strain in engineering components,
investigation

of microstructure, and grazing-incidence diffraction from
surface

layers. The beam line is built on a bending magnet, and
operates in the

energy range from 5 keV to 40 keV. After the move to an
undulator

source in 2002, it will benefit from an extented energy
range up to 60

keV and increased flux and resolution. It is anticipated
that

enhancements to the data quality will be achieved, leading
to the

solution of larger crystal structures, and improvements
in the accuracy

of refined structures. The systematic exploitation of
anisotropic

thermal expansion will help reduce the effects of peak
overlap in the

analysis of powder diffraction data.

Krimmer, B Gilles, R Zeitelhack, K
Schneider, R

Montermann, G Boysen, H Fuess,
H

A new detector system for the structure powder diffractometer SPODI
at

the FRM-II in Garching

APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 74, 2002, S154-S156.

This article describes the concept of one of the new technical features

of the structure powder diffractometer SPODI: the array
of

position-sensitive detectors including the read-out electronics.
80

single-He3 detectors each with an active length of 300
mm will be

arranged vertically in a detector bank. The position sensitivity

enables us to evaluate larger parts of the Debye-Scherrer
rings and to

improve the determination of the 2theta positions of the
Bragg peaks.

The set-up of this detector system, which is called an
individual

counter array, is described. Test measurements with the
prototype of

the read-out electronics are presented. A software package
will store

the signals in a 2D matrix and allow various evaluation
procedures of

the data.

Etc

Hundt, R Schon, JC Jansen, M

CMPZ - an algorithm for the efficient comparison of periodic structures

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006, 6-16.

The systematic comparison of the atomic structure of solid compounds

has become an important task in crystallography, chemistry,
physics and

materials science, in particular in the context of structure
prediction

and structure determination of crystalline solids. In
this work, an

efficient and robust algorithm for the comparison of periodic

structures is presented, which is based on the mapping
of the point

patterns of the two structures into each other. This algorithm
has been

implemented as the module CMPZ in the structure visualization
and

analysis program KPLOT.

Norrman, M Stahl, K Schluckebier, G
Al-Karadaghi, S

Characterization of insulin microcrystals using powder diffraction
and

multivariate data analysis

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006, 391-400.

Twelve different microcrystalline insulin formulations were

investigated by X-ray powder diffraction and were shown
to have very

characteristic patterns.

Koudelka-B; Capkova-P

Supramol - a program for structure analysis of
intercalates using molecular simulations: the structure of VOPO4.C6H4O2

JOURNAL-OF-MOLECULAR-MODELING. 2002; 8 (5) :
184-190

A method of structure analysis of intercalates
has been developed that uses a combination of molecular simulations with
powder diffraction.

Altomare A., Giacovazzo C., Ianigro M., Moliterni
AGG, Rizzi R

Peak labelling in electron density maps from
powder data: the use of crystal chemical information

J. Appl. Cryst. 35 (2002) 21-27.

Hsu-HP; Lin-SC; Hansmann-UHE

Energy landscape paving for X-ray structure determination
of organic molecules

ACTA-CRYSTALLOGRAPHICA-SECTION-A. MAY 2002; 58
Part 3 : 259-264

The new approach has been tested using the example
of 9-(methylamino)-1H-phenalen-1-one 1,4-dioxan-2-y1 hydroperoxide solvate
(C14H11NO.C4H8O4). The results indicate that, for this example, ELP outperforms
standard techniques such as simulated annealing.

Weirich-TE; Winterer-M; Seifried-S; Mayer-J

Structure of nanocrystalline anatase solved and
refined from electron powder data

ACTA-CRYSTALLOGRAPHICA-SECTION-A. JUL 2002; 58
Part 4 : 308-315

Energy-filtered Debye-Scherrer electron powder
data have been successfully employed to determine the structure of nanocrystalline
anatase (TiO2). The performed structure analysis includes determining the
unit cell, space group, solving the structure via direct methods from extracted
intensities and refining the structure using the Rietveld technique. The
result of the present study shows that the methods originally developed
for determining structures from X-ray powder data work equally well with
data from electron powder diffraction.

Middleton-DA; Peng-X; Saunders-D; Shankland-K;
David-WIF; Markvardsen-AJ

Conformational analysis by solid-state NMR and
its application to restrained structure determination from powder diffraction
data

CHEMICAL-COMMUNICATIONS. 2002; (17) : 1976-1977

Solid-state NMR is used to dramatically improve
the efficiency and reliability of molecular crystal structure determination
from X-ray powder diffraction data.

BETHANIS-K; TZAMALIS-P; HOUNTAS-A; TSOUCARIS-G

Ab initio determination of a crystal structure
by means of the Schrodinger equation

Acta-crystallographica-Section-A-Foundations-of-crystallography.
2002; 58 (p.3) : 265-269

It is shown that the use of the Schrodinger equation
may lead to the ab initio determination of the positions of the nuclei
in a crystal, given a limited number of diffracted-beam intensities.

IDA-T; TORAYA-H

Deconvolution of the instrumental functions in
powder X-ray diffractometry

Journal-of-applied-crystallography. 2002; 35
(p.1) : 58-68

S. Brenner, L.B. McCusker and C. Baerlocher,

The application of structure envelopes in structure
determination from powder diffraction data

J. Appl. Cryst. 35 (2002) 243-252.

Hao,-Q

Phasing from an envelope.

Acta-Crystallogr-D-Biol-Crystallogr. 2001 Oct;
57(Pt 10): 1410-4

D.M. Ockwell, M.A. Hough, J.G. Grossmann, S.S.
Hasnain and Q. Hao

Implementation of cluster analysis for ab initio
phasing using the molecular envelope from solution X-ray scattering

Acta Cryst. D56 (2000) 1002-1006.

Program FSEARCH

Heuer-M

The determination of site occupancies using a
new strategy in Rietveld refinements

JOURNAL-OF-APPLIED-CRYSTALLOGRAPHY, 34 (2001)
271-279

The purpose of the study reported here was to
determine if the LOT method can also be used in Rietveld refinements.

David WIF

Robust Rietveld refinement in the presence of
impurity phases

J. Appl. Cryst. 34 (2001) 691-698.

A.J. Markvardsen, W.I.F. David, J.C. Johnson &
K. Shankland,

A probabilistic approach to space-group determination
from powder diffraction data.

Acta Cryst. A57 (2001) 47-54.

Shiono-M; Takakura-H; Yamamoto-A

Ab initio structure solutions of quasicrystals
by a density modification method

FERROELECTRICS-. 2001; 250 (1-4) : 293-296

Turner GW, Tedesco E, Harris KDM, Johnston RL,
Kariuki BM

A method for understanding characteristics of
multi-dimensional hypersurfaces, illustrated by energy and powder profile
R-factor hypersurfaces for molecular crystals

Z. Kristallogr. 216 (2001) 187-189.

V.Y. Lunin, L.N. Lunina, T.E. Petrova, T.P. Skovoroda,
A.G. Urzhumtsev and A.D. Podjarny,

Low-resolution ab initio phasing: problems and
advances

Acta Cryst. D56 (2000) 1223-1232.

C.L. Henley, V. Elser and M. Mihalkovic,

Structure determinations for random-tiling quasicrystals

Z. Kristallogr. 215 (2000) 553-568.

K. Pilz and K.F. Fischer,

Solving crystal structures without Fourier mapping.
II. Non-centrosymmetric case

Z. Kristallogr. 215 (2000) 640-649.

V.I. Korsunsky,

The investigation of structure of heavy metal
clusters and polynuclear complexes in powder-samples with the radial distribution
function method

Coordination Chem. Reviews 199 (2000) 55-87.

D.I. Svergun,

Advanced solution scattering data analysis methods
and their applications

J. Appl. Cryst. 33 (2000) 530-534.

Guo-Liping; Cheng-Zhixu (China Inst. of Atomic
Energy, Beijing (China)

A profile fitting software package (CPOWDER)
and its application in powder diffraction research

Atomic-Energy-Science-and-Technology (Mar 2000)
v. 34(2) p. 120-124

Y. X. Gu, Y. D. Liu, Q. Hao and H. F. Fan

Solving crystal structures from two-wavelength
X-ray powder diffraction data - breaking the phase ambiguity in the noncentrosymmetric
case

Acta Cryst. (2000). A56, 592-595

Wessels T. Baerlocher C. McCusker LB.

Single-crystal-like diffraction data from polycrystalline
materials

Science. 284(5413):477-479, 1999.

Grosse-Kunstleve RW. McCusker LB. Baerlocher C.

Zeolite structure determination from powder diffraction
data: applications of the FOCUS method

J. Appl. Crystallogr. 32(Part 3):536-542, 1999.

Lunin VY. Lunina NL. Urzhumtsev AG.

Seminvariant density decomposition and connectivity
analysis and their application to very low resolution macromolecular phasing

Acta Crystallogr. Sect. A. 55(Part 5):916-925,
1999.

Li BH. Jin QH. Zhu SP. Guo ZY. Ding DT. Sun PC.

Development of three-dimensional, four-connected
framework structures with extra-large open pores

Microporous Mesoporous Mat. 31(1-2):123-127,
1999.

Altomare A. Giacovazzo C. Guagliardi A. Moliterni
AGG. Rizzi R.

Solving crystal structures from powder data.
V. Located molecular fragment and powder-pattern decomposition

J. Appl. Crystallogr. 32(Part 5):963-967, 1999.

Dong C. Wu F. Chen H.

Correction of zero shift in powder diffraction
patterns using the reflection-pair method

J. Appl. Crystallogr. 32(Part 5):850-853, 1999.

P. W. Stephens

Phenomenological model of anisotropic peak broadening
in powder diffraction

J. Appl. Cryst. (1999). 32, 281 - 289.

R. W. Cheary and A. A. Coelho

Axial Divergence in a Conventional X-ray Powder
Diffractometer. II. Realization and Evaluation
in a Fundamental-Parameter Profile Fitting Procedure

J. Appl. Cryst. (1998). 31, 862 - 868

P. Riello, G. Fagherazzi and P. Canton

Scale Factor in Powder Diffraction

Acta Cryst. (1998). A54, 219 - 224

Dorset DL.

DIRECT DETERMINATION OF POLYMER CRYSTAL STRUCTURES
FROM FIBRE AND POWDER X-RAY DATA

Polymer. 38 (1997) 247-253.

R. W. Grosse-Kunstleve, L. B. McCusker and Ch.
Baerlocher

Powder Diffraction Data and Crystal Chemical
Information Combined in an Automated Structure Determination Procedure
for Zeolites

J. Appl. Crystallogr. 30 (1997) 985-995.

Hammond RB. Roberts KJ. Docherty R. Edmondson
M.

COMPUTATIONALLY ASSISTED STRUCTURE DETERMINATION
FOR MOLECULAR MATERIALS FROM X-RAY POWDER DIFFRACTION DATA

Journal of Physical Chemistry B. 101 (1997) 6532-6536.

Le Bail A. Jouanneaux A.

A QUALITATIVE ACCOUNT FOR ANISOTROPIC BROADENING
IN WHOLE-POWDER-DIFFRACTION-PATTERN FITTING BY SECOND-RANK TENSORS

Journal of Applied Crystallography. 30 (1997)
265-271.

Norby P.

SYNCHROTRON POWDER DIFFRACTION USING IMAGING
PLATES - CRYSTAL STRUCTURE DETERMINATION AND RIETVELD REFINEMENT

Journal of Applied Crystallography. 30 (1997)
21-30.

Parise JB. Chen J.

STUDIES OF CRYSTALLINE SOLIDS AT HIGH PRESSURE
AND TEMPERATURE USING THE DIA MULTI-ANVIL APPARATUS

European Journal of Solid State & Inorganic
Chemistry. 34 (1997) 809-821.

Altomare A. Carrozzini B. Giacovazzo C. Guagliardi
A. Moliterni AGG. Rizzi R.

SOLVING CRYSTAL STRUCTURES FROM POWDER DATA .1.
THE ROLE OF THE PRIOR INFORMATION IN THE TWO-STAGE METHOD

Journal of Applied Crystallography, 29 (1996)
667-673.

Altomare A. Foadi J. Giacovazzo C. Guagliardi
A. Moliterni AGG.

SOLVING CRYSTAL STRUCTURES FROM POWDER DATA .2.
Etc

Journal of Applied Crystallography, 29 (1996)
674-681.

Y.G. Andreev,T. Lundsrtöm & N.I. Sorokin,

Powder diffraction pattern fitting and structure
refinement by means of the CPSR v.3.1 software package,

Nucl. Instr. & Meth. in Phys. Res. A354 (1995)
134-138.

J-J Liang, F.C. Hawthorne, M. Novak & P. Cerny,

Crystal-structure refinement of boromuscovite
polytypes using a coupled Rietveld - static-structure energy minimization
method,

The Canadian Mineralogist 33 (1995) 859-865.

R.E. Marsh,

Some thoughts on choosing the correct space group,

Acta Cryst. B51 (1995) 897-907.

M. Ohmasa and K. Ohsume,

Determination of Laue class from diffraction
data of polycrystalline materials,

Acta Cryst. A51 (1995) 87-91.

R. Peschar, H. Schenk & P. Capkova,

Preferred-orientation correction and normalization
procedure for ab initio structure determination from powder data,

J. Appl. Cryst. 28 (1995) 127-140.

P. G. Byrom & B.W. Lucas,

Crystal structure determination by neutron powder
diffraction using structural and packing constraints,

J. Appl. Cryst. 24 (1991) 1005-1008.

C.C Wilson & J.W. Wadsworth,

Crystal structure determination from low-resolution
X-ray powder diffraction data.

Acta Cryst. A46 (1990) 258-262.

C.C. Wilson,

Determination of crystal structures from poor-quality
data using Patterson methods,

Acta Cryst. A45 (1989) 833-839.

Sivia-DS; David-WIF

A Bayesian approach to phase extension

JOURNAL-OF-PHYSICS-AND-CHEMISTRY-OF-SOLIDS. DEC 2001; 62 (12) : 2119-212

David-WIF; Sivia-DS

Background estimation using a robust Bayesian analysis

JOURNAL-OF-APPLIED-CRYSTALLOGRAPHY. JUN 2001; 34 Part 3 : 318-324

Helliwell, M Jones, RH Kaucic, V
Logar, NZ

The use of softer X-rays in the structure elucidation of microporous

materials

JOURNAL OF SYNCHROTRON RADIATION 12, 2005, 420-430.

Microporous materials, such as zeolites and aluminophosphates, have

many applications as molecular sieves and shape-selective
catalysts.

This is due to their three-dimensional frameworks, which
contain

regular pores and channels, to their high acidity, arising
from

Bronsted and Lewis acid active sites, and to the incorporation
of

transition metal atoms into framework sites. This review
firstly

provides an introduction into the nature and properties
of these

materials, and their important applications; the difficulties
in their

full characterization and possible methods of elucidating
their

structures are then outlined; finally, methods of characterization,

utilizing 'softer X-rays' are introduced. The first method
is the

determination of low concentrations of transition metals,
incorporated

into the frameworks using single crystal anomalous dispersion

crystallography; synchrotron radiation is used to tune
to the

absorption edge of the metal atom in question, in order
to change its

signal relative to that of the rest of the structure,
thereby allowing

the pinpointing of its positions and the determination
of its

concentration at each site in the framework. Secondly,
the use of

longer wavelengths in powder diffraction studies is described,
which,

by stretching out the powder pattern, thereby reduces
the overlapping

of the diffraction peaks, thus allowing the structure
to be solved by

conventional direct methods. Finally, the use of X-ray
absorption

spectroscopy to determine the metal incorporation and
the nature of

coordination at the metal atom sites, in Mn silicalite-1
and FAPO-36,

are described.

Vaughan, GBM Schmidt, S Poulsen, HF

Multicrystal approach to crystal structure solution and refinement

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2005, 813-825.

We present a method in which the contributions from the individual

crystallites in a polycrystalline sample are separated
and treated as

essentially single crystal data sets. The process involves
the

simultaneous determination of the orientation matrices
of the

individual crystallites in the sample, the subsequent
integration of

the individual peaks, and filtering and summing of the
subsequent

integrated intensities, in order to arrive at a single-crystal
like

data set which may be treated normally. In order to demonstrate
the

method, we consider as a test case a small molecule structure,
cupric

acetate monohyrade. We show that it is possible to obtain
a

single-crystal quality structure solution and refinement,
in which

accurate anisotropic thermal parameters and hydrogen atom
positions are

obtained.

Brouwer, DH Darton, RJ Morris, RE
Levitt, MH

A solid-state NMR method for solution of zeolite crystal structures

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 127, 2005, 10365-10370.

Since zeolites are notoriously difficult to prepare as large single

crystals, structure determination usually relies on powder
X-ray

diffraction (XRD). However, structure solution (i.e.,
deriving an

initial structural model) directly from powder XRD data
is often very

difficult due to the diffraction phase problem and the
high degree of

overlap between the individual reflections, particularly
for materials

with the structural complexity of most zeolites. Here,
we report a

method for structure determination of zeolite crystal
structures that

combines powder XRD and nuclear magnetic resonance (NMR)
spectroscopy

in which the crucial step of structure solution is achieved
using

solid-state Si-29 double-quantum dipolar recoupling NMR,
which probes

the distance-dependent dipolar interactions between naturally
abundant

Si-29 nuclei in the zeolite framework. For two purely
siliceous zeolite

blind test samples, we demonstrate that the NMR data can
be combined

with the unit cell parameters and space group to solve
structural

models that refine successfully against the powder XRD
data.

Coelho, AA

A bound constrained conjugate gradient solution method as applied to

crystallographic refinement problems

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 455-461.

Small modifications to the conjugate gradient method for solving

symmetric positive definite systems have resulted in an
increase in

performance over LU decomposition by a factor of around
84 for solving

a dense system of 1325 unknowns. Performance is further
increased in

the case of applying upper- and lower-bound parameter
constraints. For

structure solution employing simulated annealing and the
Newton -

Raphson method of non-linear least squares, the overall
performance

gain can be a factor of four, depending on the applied
constraints. In

addition, the new algorithm with bounding constraints
often seeks out

lower minima than would otherwise be attainable without
constraints.

The behaviour of the new algorithm has been tested against
the

crystallographic problems of Pawley refinement, rigid-body
and general

crystal structure refinement.

Masciocchi, N Sironi, A

Structural powder diffraction characterization of organometallic

species: the role of complementary information

COMPTES RENDUS CHIMIE 8, 2005, 1617-1630.

X-ray powder diffraction (XRPD) has been employed in the last years
as

an active structural tool, well beyond its classical usage
in

qualitative, quantitative and microstructural analyses.
The complexity

of the materials studied by this method has steadily grown,
allowing

the full structural characterization of molecular systems,
of organic

and organometallic nature. Here we emphasize that, when
dealing with

such moderately complex molecular materials, the power
of XRPD can be

enhanced not only by increasing the radiation flux or
the instrumental

resolution, but also (and cheaply) by using additional
(experimental or

computational) information.

Hofmann, DWM Kuleshova, L

New similarity index for crystal structure determination from X-ray

powder diagrams

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 861-866.

A new similarity index for automated comparison of powder diagrams
is

proposed. In contrast to traditionally used similarity
indices, the

proposed method is valid in cases of large deviations
in the cell

constants. The refinement according to this index closes
the gap

between crystal structure prediction and automated crystal
structure

determination. The opportunities of the new procedure
have been

demonstrated by crystal structure solution of un-indexed
powder

diagrams of some organic pigments (PY111, PR181 and Me-PR170).

Trask, AV van de Streek, J Motherwell, WDS
Jones, W

Achieving polymorphic and stoichiometric diversity in cocrystal

formation: Importance of solid-state grinding, powder
X-ray structure

determination, and seeding

CRYSTAL GROWTH & DESIGN 5, 2005, 2233-2241.

Solid-state grinding is explored as a means of selectively preparing

specific stoichiometric or polymorphic modifications of
crystalline

supramolecular complexes, or cocrystals. In research involving

cocrystals of the model pharmaceutical compound caffeine
prepared via

solid-state grinding and solution crystallization, it
has been

demonstrated that these two methods of preparation are
not always

coterminous with respect to the cocrystal product obtained.
Examined

herein are the structures of five previously unreported
caffeine

cocrystals with monocarboxylic acids, including formic
acid, acetic

acid, and trifluoroacetic acid. This system illustrates
three different

possibilities in performing cocrystal preparation via
the dual methods

of solid-state grinding and solution crystallization:
(1) the same

cocrystal can result from both methods; (2) different
cocrystal

stoichiometries can result from each method; (3) different
cocrystal

polymorphs can result from each method. Materials that
at first could

be prepared only by solid-state grinding were later induced
to

crystallize from solution by seeding with the grinding
material.

Because some cocrystals from grinding contained minor
residual

unreacted starting components, a phase-subtraction method
was used to

enable subsequent crystal structure determination from
powder X-ray

diffraction data. The findings herein assign a significance
to

solid-state grinding as a technique of choice in widespread
screening

efforts for novel supramolecular materials.

Basso, S Fitch, AN Fox, GC Margiolaki,
I Wright, JP

High-throughput phase-diagram mapping via powder diffraction: a case

study of HEWL versus pH

ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY 61, 2005,
1612-1625.

44 samples of tetragonal hen egg-white lysozyme (HEWL) were obtained
as

a series of polycrystalline precipitates at 277 K and
room temperature

in the pH range between 6.56 and 3.33. The precipitates
were

investigated by the collection of high-resolution powder
X-ray

diffraction data at 295 K, which reveal the tetragonal
or orthorhombic

forms of lysozyme depending on the temperature and pH
of

crystallization. The use of a new robotic sample changer
greatly

facilitated these measurements. LeBail analyses of the
powder patterns

display a characteristic behaviour for the pH dependence
of the

tetragonal unit-cell parameters of HEWL crystallized at
both

temperatures. More detailed analysis shows that molecular
replacement

can give a suitable starting point for structural refinements,

illustrating that powder data can be sufficient for this
approach.

Pawley or Rietveld refinements that fit a single model
to four data

sets simultaneously from four samples crystallized at
pH values across

the range studied benefit from improved powder data quality
via the

anisotropic changes in the unit cell. The Rietveld analysis
gave an

average structural model with excellent goodness of fit
and

stereochemistry.

Margiolaki, I Wright, JP Fitch, AN
Fox, GC von Dreele, RB

Synchrotron X-ray powder diffraction study of hexagonal turkey

egg-white lysozyme

ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY 61, 2005,
423-432.

The structure of turkey egg-white lysozyme (TEWL) has been refined
from

high-resolution X-ray powder diffraction data. The sample
was rapidly

obtained as a polycrystalline precipitate at high protein
concentration

using 0.5 M NaCl solvent pH 6 and was deposited in the
PDB with code

1xft. The diffraction data were collected at room temperature.

Molecular replacement was shown to give a suitable starting
point for

refinement, illustrating that powder data can be sufficient
for this

approach. Crystallographic models were then refined by
combined

Rietveld and stereochemical restraint analysis of the
powder data

(d(min) = 3.35 angstrom), resulting in the extraction
of reliable

lattice parameters and the refinement of the molecular
conformation at

room temperature. The structure is hexagonal [space group
P6(1)22,

unit-cell parameters a = 71.0862 (3), c = 85.0276 (5)
angstrom] with 12

symmetry-related molecules in the unit cell, in agreement
with previous

studies. The results of our analysis are indicative of
specific amino

acids being disordered at this temperature. Upon cooling,
a sudden drop

in the lattice parameters at similar to 250 K is observed
concurrently

with the freezing of the mother liquor. The observation
of severe peak

broadening below this temperature indicates strain effects
accompanying

the freezing transition, which are found to be reversible.
Finally, a

correlation between the unit-cell parameters and the pH
of the buffer

solution is evident, in a similar manner to earlier observations
on

HEWL.

Evans, JSO Evans, IR

Beyond classical applications of powder diffraction

CHEMICAL SOCIETY REVIEWS 33, 2004, 539-547.

This article provides a short tutorial review of how laboratory powder

diffraction methods can be used to establish a variety
of

"non-traditional'' pieces of information about solid state

materials-information beyond simple phase identification
or structure

determination at a specific temperature. The examples
show how unique

insights into synthetic pathways, reaction mechanisms,
reaction

kinetics, polymorphism, phase transitions and physical
properties can

be obtained for a variety of different types of materials.

Gilmore, CJ Barr, G Paisley, J

High-throughput powder diffraction. I. A new approach to qualitative

and quantitative powder diffraction pattern analysis using
full pattern

profiles

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004, 231-242.

A new integrated approach to full powder diffraction pattern analysis

is described. This new approach incorporates wavelet-based
data

pre-processing, non-parametric statistical tests for full-pattern

matching, and singular value decomposition to extract
quantitative

phase information from mixtures. Every measured data point
is used in

both qualitative and quantitative analyses. The success
of this new

integrated approach is demonstrated through examples using
several test

data sets. The methods are incorporated within the commercial
software

program SNAP-1D, and can be extended to high-throughput
powder

diffraction experiments.

Bhuvanesh, NSP Reibenspies, JH

A novel approach to micro-sample X-ray powder diffraction using nylon

loops

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 1480-1481.

A novel method for sample mounting to obtain powder diffraction from

very small amounts of samples ( ranging from micrograms
down to a few

nanograms), by using a combination of multiwire area detector,
three-

circle diffractometer, monochromatic Cu K alpha radiation
and 10 mum

nylon loops, has been developed. This method exploits
customary single-

crystal approaches to collect the powder diffraction pattern,
which

overcomes many of the limitations of conventional powder
X- ray

diffraction.

Gozzo, F Schmitt, B Bortolamedi, T
Giannini, C Guagliardi, A

Lange, M Meister, D Maden, D
Willmott, P Patterson, BD

First experiments at the Swiss Light Source Materials Science beamline

powder diffractometer

JOURNAL OF ALLOYS AND COMPOUNDS 362, 2004, 206-217.

The Materials Science beamline at the Swiss Light Source saw 'first

light' in Spring 2001 and is presently undergoing commissioning
and

pilot experiment operation. In this article we concentrate
on one of

the three MS beamline stations, the Powder Diffractometer,
and report

on resolution tests and first experimental results. Using
the

high-resolution multi-crystal analyzer detector, full
widths at half

maximum (FWHM) smaller than 0.01degrees were measured
with standard

powders and FWHMs smaller than 0.003degrees were measured
with a single

Si(111) crystal and a very low-divergent incident beam.
With the same

detector, first residual stress measurements on low pressure
plasma

sprayed coatings were performed. Dynamic electric field-induced
strain

effects in relaxor perovskite crystals and the influence
of

water-soluble polymers on the early hydration of cement
were studied

using a fast read-out multistrip solid-state detector.

Baerlocher, C McCusker, LB Prokic, S
Wessels, T

Exploiting texture to estimate the relative intensities of overlapping

reflections

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2004, 803-812.

Additional information about the relative intensities of reflections

that overlap in a powder diffraction pattern can be obtained
from a

polycrystalline sample in which the crystallites are preferentially

oriented. If the data are collected and analyzed appropriately,
more

single-crystal-like reflection intensities can be extracted,
and

thereby more complex structures solved. This 'texture
method' was

implemented initially in reflection mode and its power
demonstrated

with the solution of the 117-atom structure of the hi-h-silica
zeolite

UTD-1F However, the experiment required a minimum of 3
days of

synchrotron beamtime per sample. In an attempt to reduce
the amount of

beamtime needed and to simplify the experiment itself,
a transmission

mode alternative using an area detector was developed.
Details of the

sample preparation, data collection and data analysis
for both

geometries are described. The solution of the structures
of the

aluminophosphates Mu-9 (R(3) over bar c, a = 14.0696(1)
Angstrom, c =

42.3113(4) Angstrom) and AIPO-M (Pbca, a = 9.7493(1) Angstrom,
b =

29.1668(2) Angstrom, c = 9.3528(1) Angstrom) using reflection
and

transmission mode data, respectively, are provided as
examples of the

method.

Habershon, S Cheung, EY Harris, KDM
Johnston, RL

An efficient algorithm for calculating whole-profile functions in

crystal structure solution from powder diffraction data

CHEMICAL PHYSICS LETTERS 390, 2004, 394-398.

A method for calculation of the whole-profile powder diffraction

R-factor R-wp, adapted specifically for use in direct-space
structure

solution, is shown to be faster by a factor of approximately
20 than

standard methods for calculating R-wp.

Dutour, J Guillou, N Huguenard, C
Taulelle, F

Mellot-Draznieks, C Ferey, G

Chiolite, a case study for combining NMR crystallography, diffraction

and structural simulation

SOLID STATE SCIENCES, 6, 2004, 1059-1067.

Chiolite has been selected as a test case for developing a general

approach to solve inorganic structures from powders by
combining NMR,

modeling, and X-ray diffraction. The different steps of
the strategy

are successfully performed, building the candidate integrant
units

using NMR, simulating candidate crystal structures using
the

computational AASBU method, and checking the consistency
of the

candidate structures against the diffraction data analyzed
with FOX

computer program.

Li, ZG Harlow, RL Foris, CM Li,
H Ma, P Vickery, RD Maurin, MB
Toby, BH

New applications of electron diffraction in the pharmaceutical

industry: Polymorph determination by using a combination
of electron

diffraction and synchrotron X-ray powder diffraction techniques

MICROSCOPY AND MICROANALYSIS 8, 2002, 134-138.

Electron diffraction has been recently used in the pharmaceutical

industry to study the polymorphism in crystalline drug
substances.

While conventional X-ray diffraction patterns could not
be used to

determine the cell parameters of two forms of the microcrystalline
GP

IIb/IIIa receptor antagonist roxifiban, a combination
of electron

single-crystal and synchrotron powder diffraction techniques
were able

to clearly distinguish the two polymorphs. The unit-cell
parameters of

the two polymorphs were ultimately determined using new
software

routines designed to take advantage of each technique's
unique

capabilities. The combined use of transmission electron
microscopy

(TEM) and synchrotron patterns appears to be a good general
approach

for characterizing complex (low-symmetry, large-unit-
cell,

micron-sized) polymorphic pharmaceutical compounds.

Brenner, S McCusker, LB Baerlocher, C

The application of structure envelopes in structure determination from

powder diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY 35, 2002, 243-252.

A structure envelope is a special type of periodic nodal surface that

separates regions of high electron density from those
of low electron

density. Once such a surface has been generated, it can
be used in

combination with direct-space methods to facilitate structure
solution

from powder data. To generate an informative structure
envelope, the

phases of the structure factors of a few strong low-order
reflections

must be determined; an algorithm has been developed for
this purpose.

The program SayPerm combines (a) the use of error-correcting
codes

(e.c.c.'s) to sample phase space efficiently, (b) a pseudo-atom

approximation of structure fragments to simulate atomic
resolution at

ca 2.5 Angstrom, and (c) phase extension and phase set
ranking using

the Sayre equation. The effect of using a structure envelope
in

structure solution was first tested in combination with
a subroutine

for finding zeolite topologies in the program FOCUS. Then
extension to

molecular structures in combination with a simulated-annealing
program

was explored. This resulted in the development of the
program Safe and

the subsequent determination of the structure of a tri-beta-peptide

(C32N3O6H53) with 17 variable torsion angles.

Brunelli, M Wright, JP Vaughan, GRM
Mora, AJ Fitch, AN

Solving larger molecular crystal structures from powder diffraction

data by exploiting anisotropic thermal expansion

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 42, 2003, 2029-2032.

Pichon, C Palancher, H Hodeau, JL
Berar, JF

Towards operando characterisation by powder diffraction techniques
of

molecular sieves

OIL & GAS SCIENCE AND TECHNOLOGY-REVUE DE L INSTITUT FRANCAIS DU
PETROLE

60, 2005, 831-848.

Working molecular sieves imply numerous and various atoms and for their

characterisation we need chemical selective probes. Thus
they can be

studied either by neutron powder diffiraction or by anomalous
X-ray

powder diffiraction techniques to extract structural information.
We

will illustrate the complementarities of these methods
in the analysis

of two different chemical processes on X-type zeolite.

In the first case, a fully exchanged barium X-type zeolite
was,

firstly, characterised by neutron powder diffiraction
after an ex situ

preparation step. During the preparation step, the sample
was saturated

with a mixture of heavy water and deuterated para-xylene.
The

selectivity of neutron diffraction for light elements
allows the

precise location of both water and xylene molecules.

In the second example, an X-type zeolite exchanged by
both strontium

and rubidium cations was studied during the dehydration
process. The in

situ structural characterisation was performed by recording,
for each

state of the zeolite (hydrated, dehydrated), three X-ray
powder

patterns. Two of them were measured at an energy close
to the

absorption edge of each compensating cation (Sr2+ and
Rb+) and one far

from both absorption edges. The chemical selectivity of
resonant

diffraction allows an accurate determination of the distribution
of

compensating cations (location, distribution and mobility)
during the

dehydration process.

Finally a comparison of some specificities and limitations
of both

methods are summarized.

Schmidt, S Poulsen, HF Vaughan, GBM

Structural refinements of the individual grains within polycrystals
and

powders

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 326-332.

A method is presented for simultaneous structural refinement of up
to

several hundred grains inside powders or polycrystals.
The method is

based on the use of hard X-rays and the indexing program
GRAINDEX,

where grain orientations are found by scanning in Euler
space.

Conventional experimental setups and refinement programs
for

single-crystal work can be applied. The method is validated
by a study

of a sintered plate of alpha-Al2O3, containing of the
order of 1500

grains in the gauge volume. 57 of the largest grains were
refined with

respect to the Al z and O x positions as well as the isotropic
atomic

displacement parameters. The R1 values were 3.4% and 3.8%
for the grain

average and the best grain, respectively. A discussion
of the potential

of the method is presented, as well as the main limitation:
grain size

and overlap of diffraction spots.

Redeterminations

Florence, AJ Shankland, N Shankland, K
David, WIF Pidcock, E

Xu, XL Johnston, A Kennedy, AR
Cox, PJ Evans, JSO

Steele, G Cosgrove, SD Frampton,
CS

Solving molecular crystal structures from laboratory X-ray powder

diffraction data with DASH: the state of the art and challenges

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 249-259.

The crystal structures of 35 molecular compounds have been redetermined

from laboratory monochromatic capillary transmission X-ray
powder

diffraction data using the simulated-annealing approach
embodied within

the DASH structure solution package. The compounds represent

industrially relevant areas ( pharmaceuticals; metal coordination

compounds; nonlinear optical materials; dyes) in which
the research

groups in this multi-centre study are active. The molecules
were

specifically selected to form a series within which the
degree of

structural complexity (i.e. degrees of freedom in the
global

optimization) increased systematically, the degrees of
freedom

increasing with increasing number of optimizable torsion
angles in the

structural model and with the inclusion of positional
disorder or

multiple fragments ( counterions; crystallization solvent;
Z' > 1). At

the lower end of the complexity scale, the structure was
solved with

excellent reproducibility and high accuracy. At the opposite
end of the

scale, the more complex search space offered a significant
challenge to

the global optimization procedure and it was demonstrated
that the

inclusion of modal torsional constraints, derived from
the Cambridge

Structural Database, offered significant benefits in terms
of

increasing the frequency of successful structure solution
by

restricting the magnitude of the search space in the global

optimization.

Graphism

Hinrichsen, B Dinnebier, RE Jansen, M

Powder3D: An easy to use program for data reduction and graphical

presentation of large numbers of powder diffraction patterns

ZEITSCHRIFT FUR KRISTALLOGRAPHIE suppl 23, part 1, 2006, 231-236.

The presented software facilitates data reduction of multiple powder

diffraction patterns. Many operations are automated for
the application

to huge sets of patterns collected during diffraction
experiments in

dependence of time, temperature, pressure and composition.
The features

include basic data reduction procedures, such as background
reduction,

K-alpha stripping, smoothing and Le Bail fitting. Many
file formats are

supported to provide interoperability with GSAS, Fullprof
and Crysfire

(amongst others). The software is freely available for
non-profit use

at http://www.fkf.mpg.de/xray/.

Rietveld, DDM

Toby, BH

R factors in Rietveld analysis: How good is good enough?

POWDER DIFFRACTION 21, 2006, 67-70.

The definitions for important Rietveld error indices are defined and

discussed. It is shown that while smaller error index
values indicate a

better fit of a model to the data, wrong models with poor
quality data

may exhibit smaller values error index values than some
superb models

with very high quality data.

Solovyov, LA

Full-profile refinement by derivative difference minimization

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004, 743-749.

A new method of full-profile refinement is developed on the basis of

the minimization of the derivatives of the pro le difference
curve. The

use of the derivatives instead of the absolute difference
between the

observed and calculated pro le intensities allows refinement

independently of the background. The procedure is tested
on various

powder diffraction data sets and is shown to be fully
functional.

Besides having the capability of powder diffraction structure
analysis

without modelling the background curve, the method is
shown to allow

the derivation of structure parameters of even higher
quality than

those obtained by Rietveld refinement in the presence
of systematic

errors in the model background function. The derivative
difference

minimization principles may be used in many different
areas of powder

diffraction and beyond.

Dusek, M Petricek, V

Three years of developing JANA2000 305, 2004, 267-271.

FERROELECTRICS

We present the latest state of the computing system JANA2000. The main

improvement comparing with the previous version JANA98
consists in the

possibility to use powder diffraction data of one or more

three-dimensional or modulated phases. The current development
of

JANA2000 comprises (1) generalization of the program from
four to six

dimensions, (2) improvement of the powder option, (3)
developing of

complex tools for transformations and (4) automatic determination
of

the (super)space symmetry.

David, WIF

On the equivalence of the Rietveld method and the correlated integrated

intensities method in powder diffraction

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004, 621-628.

The Rietveld method is the most straightforward and statistically

correct approach for the refinement of crystal structure
parameters

from powder diffraction data. The equivalent two-stage
approach,

involving the refinement of structural parameters based
on integrated

intensities extracted using the Pawley method, is extremely
useful in

circumstances such as the global optimization methods
of structure

determination, where a great many refinements need to
be performed very

quickly. The equivalence is emphasized in a simple mathematical

relationship between the goodness of fits obtained in
Rietveld, Pawley

and correlated integrated intensities refinements. A rationale
is given

for determining the estimated standard deviations for
structural

variables from powder diffraction data.

David, WIF

Powder diffraction: Least-squares and beyond

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND

TECHNOLOGY 109, 2004, 107-123.

This paper addresses some of the underlying statistical assumptions
and

issues in the collection and refinement of powder diffraction
data.

While standard data collection and Rietveld analysis have
been

extremely successful in providing structural information
on a vast

range of materials, there is often uncertainty about the
true accuracy

of the derived structural parameters. In this paper, we
discuss a

number of topics concerning data collection and the statistics
of data

analysis. We present a simple new function, the cumulative
chi-squared

distribution, for assessing regions of misfit in a diffraction
pattern

and introduce a matrix which relates the impact of individual
points in

a powder diffraction pattern with improvements in the
estimated

standard deviation of refined parameters. From an experimental

viewpoint, we emphasise the importance of not over-counting
at

low-angles and the routine use of a variable counting
scheme for data

collection. Data analysis issues are discussed within
the framework of

maximum likelihood, which incorporates the current least-squares

strategies but also enables the impact of systematic uncertainties
in

both observed and calculated data to be reduced.

Shankland, K

Global Rietveld refinement

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND

TECHNOLOGY 109, 2004, 143-154.

Global optimisation methods of structure determination from powder

diffraction data have risen to prominence in a relatively
short space

of time and they now constitute a key approach in the
examination of

polycrystalline molecular organic materials. A correctly
formulated

global optimisation approach may be regarded as a "global
Rietveld

refinement" that is capable of delivering accurate crystal
structures

from high-quality powder diffraction data. This paper
focuses on how

accuracy at all stages of a powder diffraction experiment
impacts upon

the overall structure solution process and particular
attention is paid

to assessing the degree of accuracy with which structures
are returned

from the global optimisation process.

Izumi, F

Beyond the ability of Rietveld analysis: MEM-based pattern fitting

SOLID STATE IONICS 172, 2004, 1-6.

A multipurpose pattern-fitting program, RIETAN-2000, and a software

package, VENUS, for three-dimensional (3D) visualization
were

substantially combined to grow into an integrated system
for

whole-pattern fitting (w.p.f) based on the maximum entropy
method

(MEM). In MEM-based pattern fitting (MPF), 'observed'
structure factors

resulting from Rietveld analysis are analyzed by MEM to
yield improved

structure factors, F-c(MEM). Then, we carry out w.p.f
where structure

factors are fixed at the F-c(MEM)s. F-o(w.p.f) data estimated
after

w.p.f. are analyzed again by MEM. MEM analysis and w.p.f
are

alternately repeated until R factors in the latter no
longer decrease.

These iterative processes enable us to minimize a bias
imposed by a

structural model for the Rietveld analysis on final electron/nuclear

densities. MPF is flexible enough to be capable of modeling
static and

dynamic disorder, chemical bonds, nonlocalized electrons,
and

anharmonic thermal motion better than the Rietveld method.
Applications

of MPF to structure refinements of five compounds with
disordered

structures have demonstrated its excellent performance
and

effectiveness.

Izumi, F Kumazawa, S Ikeda, T Hu,
WZ Yamamoto, A Oikawa, K

MEM-based structure-refinement system REMEDY and its applications

EPDIC 7: EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2

MATERIALS SCIENCE FORUM 378-3, 2001, 59-64.

A Rietveld-analysis program RIETAN was combined with MEED for a

maximum-entropy method (MEM) to grow into an integrated
software

REMEDY. At first, 'observed' structure factors, F-o, estimated
after

Rietveld analysis are analyzed by the MEM to give electron/nuclear

densities biased by a structural model. Then, we evaluate
structure

factors, (FeMEM)-M-(), by the Fourier transform of the
densities and

fit the whole powder pattern calculated from the F-e(MEM)
data to the

observed one to refine parameters irrelevant to the structure.
F-o data

obtained in such a manner are analyzed again by the MEM.
MEM analysis

and whole-pattern fitting are alternately repeated until
R factors in

the pattern fitting no longer decrease. REMEDY was utilized
to

investigate (a) positional disorder of K+ ions interlayered
in

KxTi2-x/3Li(x)/O-3(4), (b) atomic arrangement of K clusters
in K-type

LTA, and (c) nuclear/electron-density distribution in
HgBa2CUO4+delta.

Izumi, F

Development and applications of the pioneering technology of structure

refinement from powder diffraction data

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 111, 2003, 617-623.

A couple of Rietveld-analysis programs, RIETAN, for angle-dispersive

diffraction and time-of-flight neutron diffraction have
been

extensively used for structural studies of many compounds.
The history

of their developments is briefly reviewed. The latest
versions,

RIETAN-2000 for angle-dispersive diffraction and RIETAN-2001T
for the

Vega and Sirius diffractometers at KENS have a practical
feature of

partial profile relaxation. In this technique, primary
profile

parameters of (nearly) isolated reflections can be individually
refined

independent of secondary profile parameters. It was combined
with split

profile functions to improve fits between observed and
calculated

patterns, particularly in samples exhibiting anisotropic
profile

broadening and reflections with very large lattice-plane
spacings.

RIETAN-2000 and our own program for the maximum-entropy
method (MEM),

PRIMA, were virtually integrated into a structure-refinement
system,

REMEDY, whereby the pattern calculated from structure
factors obtained

by MEM is fit to the whole observed pattern. 'Observed'
structure

factors estimated at the end of the whole-pattern fitting
are analyzed

again by MEM. Whole-pattern fitting and MEM analysis are
alternately

repeated until R factors in the former no longer decrease.
Applications

of this technology to three inorganic compounds having
highly

disordered structures are demonstrated, showing its excellent

performance and effectiveness.

Jouanneaux, A Le Gonidec, X Fitch, AN

WinMProf: Visual Rietveld software

EPDIC 7: EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2

MATERIALS SCIENCE FORUM 378-3, 2001, 112-117.

WinMProf is a Windows application that can be used for powder

diffraction analysis, with data collected at constant
wavelength, using

the MPROF Rietveld refinement routine. The main features
of the

software are described in detail.

energy-dispersive X-ray diffraction

Dong, YH Liu, J Li, YC Li, XD

A full-pattern fitting algorithm for energy-dispersive X-ray diffraction

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 1123-1127.

A full-pattern fitting algorithm for energy-dispersive X-ray

diffraction is proposed, especially for high-pressure
X-ray diffraction

studies. The algorithm takes into account the errors in
measuring the

energy and the diffraction angle. A lognormal function
is introduced to

represent the background. All the peaks that are detectable
in the

diffraction spectra, including fluorescence and diffraction
peaks, are

considered together. Because all the data points in the
spectra are

used, the accuracy of the cell parameters obtained by
this method is

very high. This is very helpful in the analysis of the
equation of

state and the identification of new phases under high
pressure.

Size-strain, faulting

Masson, O Dooryhee, E Fitch, AN

Instrument line-profile synthesis in high-resolution synchrotron powder

diffraction

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 286-294.

An accurate method for synthesizing the instrumental line profile of

high-resolution synchrotron powder diffraction instruments
is

presented. It is shown that the instrumental profile can
be modelled by

the convolution of four physical aberration functions:
the equatorial

intensity distribution, the monochromator and analyser
transfer

functions, and the axial divergence aberration function.
Moreover, each

equatorial aberration is related to an angle-independent
function by a

scale transform factor. The principles of the instrument
line-profile

calculation are general. They are applied in the case
of the

angle-dispersive powder X-ray diffraction beamline BM16
at the ESRF.

The effects of each optical element on the overall instrument
profile

are discussed and the importance of the quality of the
different

optical elements of the instrument is emphasized. Finally,
it is shown

that the high resolution combined with the precise modelling
of the

instrument profile shape give access to a particle size
as large as 3

mum.

Kaszkur, Z Mierzwa, B Pielaszek, J

Ab initio test of the Warren-Averbach analysis on model palladium

nanocrystals

JOURNAL OF APPLIED CRYSTALLOGRAPHY 38, 2005, 266-273.

Model powder diffraction patterns were calculated via the Debye formula

from atom positions of a range of energy-relaxed closed-shell

cubooctahedral clusters. The energy relaxation employed
the Sutton-Chen

potential scheme with parameters for palladium. The assumed
cluster

size distribution followed lognormal distribution of a
crystallite

volume centred with the diameter of 5 nm, as well as two
bimodal

lognormal distributions centred around 4 nm and 7 nm.
These models

allowed an in-depth analysis of the Warren - Averbach
method of

separating strain and size effects in a peak shape Fourier
analysis.

The atom-displacement distribution in the relaxed clusters
could be

directly computed, as well as the strain Fourier coefficients.
The

results showed that in the case of the unimodal size distribution,
the

method can still be successfully used for obtaining the
column length

distribution. However, the strain Fourier coefficients
obtained from

three reflections ( 002, 004 and 008) cannot be reliably
estimated with

the Warren - Averbach method. The primary cause is a non-Gaussian

strain distribution and a shift of the diffraction maximum,
inherent to

the nanoparticles, differing for every constituent cluster
in the size

distribution. For the bimodal size distributions, the
obtained column

length distributions tend to be shifted towards the centres
of the

modes and are less sensitive to the larger size mode.

Balzar, D Audebrand, N Daymond, MR
Fitch, A Hewat, A Langford, JI

Le Bail, A Louer, D Masson, O
McCowan, CN Popa, NC Stephens, PW

Toby, BH

Size-strain line-broadening analysis of the ceria round-robin sample

JOURNAL OF APPLIED CRYSTALLOGRAPHY 37, 2004, 911-924.

The results of both a line-broadening study on a ceria sample and a

size - strain round robin on diffraction line-broadening
methods, which

was sponsored by the Commission on Powder Diffraction
of the

International Union of Crystallography, are presented.
The sample was

prepared by heating hydrated ceria at 923 K for 45 h.
Another ceria

sample was prepared to correct for the effects of instrumental

broadening by annealing commercially obtained ceria at
1573 K for 3 h

and slowly cooling it in the furnace. The diffraction
measurements were

carried out with two laboratory and two synchrotron X-ray
sources, two

constant-wavelength neutron and a time-of-flight (TOF)
neutron source.

Diffraction measurements were analyzed by three methods:
the model

assuming a lognormal size distribution of spherical crystallites,

Warren-Averbach analysis and Rietveld refinement. The
last two methods

detected a relatively small strain in the sample, as opposed
to the

first method. Assuming a strain-free sample, the results
from all three

methods agree well. The average real crystallite size,
on the

assumption of a spherical crystallite shape, is 191 (5)
Angstrom. The

scatter of results given by different instruments is relatively
small,

although significantly larger than the estimated standard

uncertainties. The Rietveld refinement results for this
ceria sample

indicate that the diffraction peaks can be successfully
approximated

with a pseudo-Voigt function. In a common approximation
used in

Rietveld refinement programs, this implies that the size-broadened

profile cannot be approximated by a Lorentzian but by
a full Voigt or

pseudo-Voigt function. In the second part of this paper,
the results of

the round robin on the size - strain line-broadening analysis
methods

are presented, which was conducted through the participation
of 18

groups from 12 countries. Participants have reported results
obtained

by analyzing data that were collected on the two ceria
samples at seven

instruments. The analysis of results received in terms
of coherently

diffracting, both volume-weighted and area-weighted apparent
domain

size are reported. Although there is a reasonable agreement,
the

reported results on the volume-weighted domain size show
significantly

higher scatter than those on the area-weighted domain
size. This is

most likely due to a significant number of results reporting
a high

value of strain. Most of those results were obtained by
Rietveld

refinement in which the Gaussian size parameter was not
refined, thus

erroneously assigning size-related broadening to other
effects. A

comparison of results with the average of the three-way
comparative

analysis from the first part shows a good agreement.

Estevez-Rams, E Leoni, M Scardi, P
Aragon-Fernandez, B Fuess, H

On the powder diffraction pattern of crystals with stacking faults

PHILOSOPHICAL MAGAZINE 83, 2003, 4045-4057.

The so-called direct solution of the powder diffraction pattern for
a

faulted layered crystal is discussed. It is shown how,
in the general

case, peak profiles can be split into a symmetric and
an antisymmetric

component. The relationships between peak profile parameters
and the

underlying faulting structure, as given by the probability
correlation

function, are evidenced. The formalism reduces to known
equations when

applied to particular faulting models. Warren's equations
for peak

profile of fcc materials with {111} planar faulting are
derived within

the framework of a general theory. Possible strategies
for

incorporating the proposed formalism into a general powder
pattern

refinement procedure are also discussed.

Cervellino, A Giannini, C Guagliardi, A

Determination of nanoparticle structure type, size and strain

distribution from X-ray data for monatomic f.c.c.-derived

non-crystallographic nanoclusters

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 1148-1158.

Whole-profile-fitting least-squares techniques are applied to simulated

and experimental X-ray diffraction patterns of monatomic
face-centred

cubic (f.c. c.)derived non-crystallographic nanoclusters
to extract

structure and size information. Three main structure types
have been

considered (cuboctahedral, icosahedral and decahedral).
Nanocluster

structure models have been generated within an original
mathematical

approach so as to be independent of a specific material.
For each

structure type, a log-normal size distribution is assumed
and a

phenomenological function is introduced to model possible
additional

size-related strain effects. The Debye function method
(modified to

increase computational efficiency) has been used to obtain
the

diffracted intensities of the nanocluster. Tests revealed
the

effectiveness of the method to recognize the structure
types correctly

and to estimate with good accuracy structure concentrations
and size

distributions. Application to a thiol-passivated gold
nanoparticle

sample is presented.

Scardi, P Leoni, M

Whole powder pattern modelling

ACTA CRYSTALLOGRAPHICA SECTION A 58, 2002, 190-200.

A new approach for the modelling of diffraction patterns without using

analytical profile functions is described and tested on
ball milled

f.c.c. Ni powder samples. The proposed whole powder pattern
modelling

(WPPM) procedure allows a one-step refinement of microstructure

parameters by a direct modelling of the experimental pattern.
Lattice

parameter and defect content, expressed as dislocation
density, outer

cut-off radius, contrast factor, twin and deformation
fault

probabilities), can be refined together with the parameters
(mean and

variance) of a grain-size distribution. Different models
for lattice

distortions and domain size and shape can be tested to
simulate or

model diffraction data for systems as different as plastically
deformed

metals or finely dispersed crystalline powders. TEM pictures
support

the conclusions obtained by WPPM and confirm the validity
of the

proposed procedure.

parallel beam with laboratory instrument

Whitfield, PS

Use of double Gobel mirrors with high-temperature stages for powder

diffraction - a strategy to avoid severe intensity fade

JOURNAL OF APPLIED CRYSTALLOGRAPHY 36, 2003, 926-930.

This paper describes an approach for countering an issue that can occur

when using a high-temperature stage with a diffractometer
equipped with

double Gobel mirrors. The optical characteristics of the
dual-mirror

configuration make it more susceptible to intensity loss
with sample

displacement than conventional parallel-beam secondary
optics. This

issue has been apparent in the use of a high-temperature
stage on a

diffractometer equipped with dual mirrors, where data
could not be

obtained from the full room temperature to 1273 K range
without

resetting the sample height manually part way through
the experiment. A

simple technique involving controlled contouring of the
sample surface

has been demonstrated to allow data to be collected uninterrupted
over

the full temperature range, while retaining satisfactory
intensities.

The extent to which this technique extends the tolerable
sample

displacement range has been quantified using a computer-controlled
XYZ

stage.

Texture

Morales, M Chateigner, D Lutterotti, L
Ricote, J

X-ray combined QTA using a CPS applied to a ferroelectric ultrastructure

TEXTURES OF MATERIALS, PTS 1 AND 2 MATERIALS SCIENCE FORUM 408-4, 2002,
113-118.

The new combined methodology for quantitative description of texture,

structure and other microstructural parameters of thin
layers using

X-ray diffraction is presented and applied to the case
of a

ferroelectric thin film of Pb0.76Ca0.24TiO3 on a Pt/TiO2/SiO2/Si

substrate. The approach allows the quantitative texture
analysis of the

ferroelectric thin film and the Pt electrode, refining
simultaneously

their structure, layers thickness, mean crystallite size
and

microstrain state. The layer thickness determination is
estimated by

the refinement of the thicknesses inserted in the absorption
and

volumic correction factors. The powerfulness of this methodology
is

discussed and compared with other approaches.

Modulated structures

Dusek, M Petricek, V Wunschel, M
Dinnebier, RE van Smaalen, S

Refinement of modulated structures against X-ray powder diffraction

data with JANA2000

JOURNAL OF APPLIED CRYSTALLOGRAPHY 34, 2001, 398-404.

JANA is a computer program for the refinement and analysis of periodic

and aperiodic (incommensurately modulated structures and
composite

crystals) crystal structures. Here a new module is introduced
that

allows Rietveld refinements against powder diffraction
data. It is

shown that JANA2000 provides a state-of-the-art description
of the peak

profiles. A re-analysis of the low-temperature structure
of (CO)(x)C-60

showed that the application of icosahedral symmetry restrictions
to the

C-60 molecule leads to a better description of the electron
density and

to a corrected position of the CO molecule as compared
with a

rigid-body refinement. The incommensurately modulated
structure of

NbTe4 has been successfully refined against X-ray powder
diffraction

data. The structural parameters are equal to, but less
accurate, than

the parameters obtained from a single-crystal study.

Electron crystallography

Weirich, TE Portillo, J Cox, G
Hibst, H Nicolopoulos, S

Ab initio determination of the framework structure of the heavy-metal

oxide CsxNb2.54W2.46O14 from 100 kV precession electron
diffraction data

ULTRAMICROSCOPY 106, 2006, 164-175.

The present work deals with the ab initio determination of the heavy

metal framework in Cs-x(Nb, W)(5)O-14 from precession
electron

diffraction intensities. The target structure was first
discovered by

Lundberg and Sundberg [Ultramicroscopy 52 (1993) 429-435],
who

succeeded in deriving a tentative structural model from
high-resolution

electron microsopy (HREM) images. The metal framework
of the compound

was solved in this investigation via direct methods from
hk0 precession

electron diffraction intensities recorded with a Philips
EM400 at 100

kV. A subsequent (kinematical) least-squares refinement
with electron

intensities yielded slightly improved co-ordinates for
the I I heavy

atoms in the structure. Chemical analysis of several crystallites
by

EDX is in agreement with the formula Cs0.44Nb2.54W2.46O14.
Moreover,

the structure was independently determined by Rietveld
refinement from

X-ray powder data obtained from a multi-phasic sample.
The compound

crystallises in the orthorhombic space group Pbam with
refined lattice

parameters a = 27.145(2), b = 21.603(2), and c = 3.9463(3)
angstrom.

Comparison of the framework structure from electron diffraction
with

the result from Rietveld refinement shows an average agreement
for the

heavy atoms within 0.09 angstrom.

Weirich, TE

First-principles calculations as a tool for structure validation in

electron crystallography

ACTA CRYSTALLOGRAPHICA SECTION A 60, 2004, 75-81.

The crystal structures of Ti11Se4 [Weirich, Ramlau, Simon, Hovmoller
&

Zou ( 1996). Nature ( London), 382, 144 - 146] and Ti45Se16
[ Weirich (

2001). Acta Cryst. A57, 183 - 191] determined previously
from

selected-area electron diffraction ( SAED) data have been
checked for

their correctness by means of total energy calculations
within the

non-local density functional theory. The reliability of
the used method

was verified by test calculations carried out for the
structurally

related compound Ti8Se3, which is well known from single-crystal
X-ray

diffraction [ Weirich, Pottgen & Simon ( 1996). Z.
Kristallogr. 212,

929 - 930]. For Ti8Se3, structural models from both experiment
and

calculation show a perfect match (average agreement 0.01
Angstrom).

This proves that the geometrical optimized models from
first-principles

calculation can be used as a reliable alternative when
good-quality

X-ray results cannot be obtained. Calculations carried
out for the two

structures determined from electron crystallography yielded
average

improvement of the atomic coordinates of 0.04 and 0.09
Angstrom for

Ti11Se4 and Ti45Se16, respectively. The optimized cell
parameters of

the monoclinic structures ( both space group C2/m, No.
12) are a =

25.51, b = 3.43, c = 19.19 Angstrom, beta = 117.9degrees
for Ti11Se4

and a = 36.31, b = 3.45, c = 16.59 Angstrom, beta = 92.1degrees
for

Ti45Se16. These results prove that crystals that are too
small for

single-crystal X-ray diffraction and are difficult to
solve by powder

diffraction may nevertheless be amenable to accurate structure

determination by electron diffraction structure analysis
using data

from standard SAED and the assumption of quasi-kinematical
scattering.

Moreover, this study shows that geometry optimization
by

first-principles calculations is the perfect tool for
validation and

improvement of complex structural models, which are suspected
to have

errors owing to the poor quality of experimental data.

Zou, XD Mo, ZM Hovmoller, S Li,
XZ Kuo, KH

Three-dimensional reconstruction of the nu-AlCrFe phase by electron

crystallography

ACTA CRYSTALLOGRAPHICA SECTION A 59, 2003, 526-539.

The three-dimensional (3D) structure of the huge quasicrystal

approximant nu-AlFeCr (space group P6(3)/m, a = 40.687
and c = 12.546

Angstrom) was solved by electron crystallography. High-resolution

transmission-electron-microscopy (HREM) images and selected-area

electron diffraction patterns from 13 different zone axes
were combined

to give a 3D potential map. 124 out of 129 unique atoms
were found in

the 3D map. Procedures for ab initio structure determination
by 3D

reconstruction are given. It is demonstrated that 3D reconstruction

from HREM images is very powerful for solving structures
- even very

complicated ones. There is no limit in terms of the number
of unique

atoms in a structure that can be solved by 3D reconstruction.

Dorset, DL

Applications of direct methods for structure determination to problems

in electron and x-ray fibre diffraction of polymers

REPORTS ON PROGRESS IN PHYSICS 66, 2003, 305-338.

In this review, the prospect of determining polymer crystal structures

directly from single crystal electron or x-ray powder/fibre
diffraction

intensity data is explored. When care is taken to collect
the best data

set from a polymer, i.e. sampling the most intense regions
of the

three-dimensional reciprocal lattice, structure analyses
can be carried

out effectively by the conventional direct phasing methods
employed in

small molecule crystallography, even though the data sets
are

relatively small. This means that constraints imposed
by multiple beam

interactions in electron diffraction and reflection overlap
in x-ray

diffraction often do not limit the structure analysis.

Several three-dimensional single crystal electron diffraction
structure

analyses are presented to illustrate the problems encountered.
These

include: polyethylene, poly(epsilon-caprolactone), isotactic

poly(butene-1) form III, isotactic polypropylene

beta-form,poly(p-oxybenzoate) and poly(ethylene sulfide).
Techniques

for sampling the complete reciprocal lattice are discussed.
If an

adequate number of data is collected, it is also possible
to refine the

structure by constrained least squares. In any case Fourier
refinement

is always useful.

From powder x-ray diffraction the crystal structure of
polyethylene has

been determined by direct methods; from fibre x-ray intensities,
this

review reports the direct analyses of poly(epsilon-caprolactone),

poly(ethylene terephthalate) and poly(tetramethyl-p-silphenylene

siloxane). Rietveld methods might also be useful for the
structure

refinement.

Direct structure analyses are advantageous in that they
circumvent a

priori assumptions about the molecular model and also
the linkage bonds

to base conformational refinement. Instead, individual
atomic positions

or molecular envelopes are observed directly in potential
or electron

density maps, to which the model can then be fit, a situation
analogous

to current practice in protein crystallography.

Dorset, DL

Correlations, convolutions and the validity of electron crystallography

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 218, 2003, 237-147.

Although often an object of controversy, electron crystallography has

emerged as a useful technique for characterization of
the

microcrystalline state, capable of elucidating crystal
structures of

unknown substances. Despite the complicated multiple scattering

perturbations to diffracted intensities, experimental
conditions can be

adjusted to favor data collection where the experimental
Patterson

function still resembles the autocorrelation function
of the actual

crystal structure. Satisfying this condition is often
sufficient to

permit structure solution from such data by direct methods.
While the

application to organic structures may seem obvious, there
are

surprising successes with data sets from inorganic materials.
The

account given in this paper, in part, portrays work leading
to the A.

L. Patterson Award to the author from the American Crystallographic

Association.

Kolb, U Matveeva, GN

Electron crystallography on polymorphic organics

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 218, 2003, 259-268.

Organic materials, such as non-linear optical active compounds

(1-(2-furyl)-3-(4-aminophenyl)-2-propene-1-one (FBAPPO)
and

1-(2-furyl)-3-(4-benzamidophenyl)-2-propene-1-one (FAPPO)),
polymeric

materials like the metal coordinated polyelectrolyte (Fe(II)
[ditopic

bis-terpyridin] (MEPE)) or polymorphic materials (e.g.

Cu-phthalocyanine), which do not crystallize big enough
for single

crystal x-ray structure analysis have been investigated
by electron

diffraction (ED) at 100 and 300 kV acceleration voltage.
Sample

preparation (direct crystallization, ultra sonication,
ultra

microtomy), diffraction strategies (selected area diffraction,
nano

diffraction, use of double-tilt rotation holder), data
collection and

data processing as well as structure solution strategies
have been

chosen dependent on the different requirements of the
compounds under

investigation. Structure analysis was carried out by simulation
using

ab initio quantum-mechanical methods like density functional
theory

(DFT), semi-empirical approach (MNDO/AM1/PM3) and force
field packing

energy calculations (DREIDING). The structure models resulting
from

simulation were refined kinematically as rigid bodies.
Subsequently,

refinements by multi-slice least squares (MSLS) procedures
taking

dynamical scattering into account were performed. The
described

combination of different methods which was used successfully
on

crystallizable materials is also adaptable to insoluble
organic

materials (e.g. pigments) and polymorphic systems.

NMR

Elena, B Pintacuda, G Mifsud, N
Emsley, L

Molecular structure determination in powders by NMR crystallography

from proton spin diffusion

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128, 2006, 9555-9560.

The inability to determine molecular structures from powdered samples

is a key barrier to progress in many areas of molecular
and materials

science. We report an approach to structure determination
that combines

molecular modeling with experimental spin diffusion data
obtained from

the high-resolution solid-state nuclear magnetic resonance
of protons,

and which allows the determination of the three-dimensional
structure

of an organic compound, in powder form and at natural
isotopic

abundance.

Senker, J Seyfarth, L Voll, J

Determination of rotational symmetry elements in NMR crystallography

SOLID STATE SCIENCES 6, 2004, 1039-1052.

In this work we present a consistent set of NMR experiments including

high-resolution as well as wideline techniques, which
allow to

determine crystallographic rotational symmetry elements
in crystalline

solids. I D spectra acquired with fast sample spinning
about the magic

angle provide the number of crystal lographically inequivalent
nuclei.

By making use of the anisotropic properties of the chemical
shift

interaction the sets of crystallographically equivalent
nuclei can be

divided into subgroups of magnetically equivalent spins
by means of

radio-frequency-driven spin-diffusion wide-line exchange
experiments.

Maximum information can be achieved from these experiments
by a

combination of time- and frequency- domain analyses. We
could

demonstrate that the number of subgroups is equal to the
order of the

rotational symmetry element in which the crystallographically

equivalent nuclei are arranged. From the evolution of
the polarisation

transfer as a function of the mixing time distances of
these spins can

be estimated quite accurately. Furthermore, it is often
possible to

distinguish between rotation and rotoinversion axes. The
potential of

this strategy for ab initio structure determination is
demonstrated on

the crystal structure of triphenyl phosphite, where eighteen
molecules

are arranged in a R-centred trigonal unit cell.

Harris, RK

NMR crystallography: the use of chemical shifts

SOLID STATE SCIENCES 6, 2004, 1025-1037.

Measurements of chemical shifts obtained from magic-angle spinning
NMR

spectra (together with quantum mechanical computations
of shielding)

can provide valuable information on crystallography. Examples
are given

of the determination of crystallographic asymmetric units,
of molecular

symmetry in the solid-state environment, and of crystallographic
space

group assignment. Measurements of full tensor components
for (199)Ha

have given additional coordination information. The nature
of

intermolecular hydrogen bonding in cortisone acetate polymorphs
and

solvates is obtained from chemical shift information,
also involving

measurement of the full tensor parameters. The resulting
data have been

used as restraints, built into the computation algorithm,
in the

analysis of powder diffraction patterns to give full crystal

structures. A combination of quantum mechanical computation
of

shielding and measurement of proton chemical shifts (obtained
by

high-speed MAS) leads to the determination of the position
of a proton

in an intermolecular hydrogen bond. A recently-developed
computer

program specifically based on crystallographic repetition
has been

shown to give acceptable results. Moreover, NMR chemical
shifts can

distinguish between static and dynamic disorder in crystalline

materials and can be used to determine modes and rates
of molecular

exchange motion.

Middleton, DA Peng, X Saunders, D
Shankland, K

David, WIF Markvardsen, AJ

Conformational analysis by solid-state NMR and its application to

restrained structure determination from powder diffraction
data

CHEMICAL COMMUNICATIONS 17, 2002, 1876-1977.

Solid-state NMR is used to dramatically improve the efficiency and

reliability of molecular crystal structure determination
from X-ray

powder diffraction data.

Femtosecond

Miao, JW Chapman, HN Kirz, J Sayre,
D Hodgson, KO

Taking X-ray diffraction to the limit: Macromolecular structures from

femtosecond X-ray pulses and diffraction microscopy of
cells with

synchrotron radiation

ANNUAL REVIEW OF BIOPHYSICS AND BIOMOLECULAR STRUCTURE 33, 2004, 157-176.

Recent work is extending the methodology of X-ray crystallography to

the structure determination of noncrystalline specimens.
The phase

problem is solved using the oversampling method, which
takes advantage

of "continuous" diffraction patterns from noncrystalline
specimens.

Here we review the principle of this newly developed technique
and

discuss the ongoing experiments of imaging nonperiodic
objects, such as

cells and cellular structures, using coherent and bright
X rays

produced by third-generation synchrotron sources. In the
longer run,

the technique may be applicable to image single biomolecules
using

anticipated X-ray free electron lasers. Here, computer
simulations have

so far demonstrated two important steps: (a) by using
an extremely

intense femtosecond X-ray pulse, a diffraction pattern
can be recorded

from a macromolecule before radiation damage manifests
itself; and (b)

the phase information can be retrieved in an ab initio
fashion from a

set of calculated noisy diffraction patterns of single
protein

molecules.

PDF

Juhas, P Cherba, DM Duxbury, PM
Punch, WF Billinge, SJL

Ab initio determination of solid-state nanostructure

NATURE 440, 2006, 655-658.

Advances in materials science and molecular biology followed rapidly

from the ability to characterize atomic structure using
single

crystals(1-4). Structure determination is more difficult
if single

crystals are not available(5). Many complex inorganic
materials that

are of interest in nanotechnology have no periodic long-range
order and

so their structures cannot be solved using crystallographic
methods(6).

Here we demonstrate that ab initio structure solution
of these

nanostructured materials is feasible using diffraction
data in

combination with distance geometry methods. Precise, sub-angstrom

resolution distance data are experimentally available
from the atomic

pair distribution function (PDF)(6,7). Current PDF analysis
consists of

structure refinement from reasonable initial structure
guesses(6,7) and

it is not clear, a priori, that sufficient information
exists in the

PDF to obtain a unique structural solution. Here we present
and

validate two algorithms for structure reconstruction from
precise

unassigned interatomic distances for a range of clusters.
We then apply

the algorithms to find a unique, ab initio, structural
solution for

C-60 from PDF data alone. This opens the door to sub-angstrom

resolution structure solution of nanomaterials, even when

crystallographic methods fail.

Bruhne, S Sterzel, R Uhrig, E Gross,
C Assmus, W

Medium range real atomic structure of face-centred icosahedral

Ho9Mg26Zn65

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 219, 2004, 245-258.

A complementary approach to quasicrystalline atomic structures in

3-dimensional (3D) real space is presented: The atomic
pair

distribution function (PDF) of face centred icosahedral
Ho9Mg26Zn65

[a(6D) = 2 x 5.18(3) Angstrom] has been obtained from
in-house powder

X-ray diffraction data (MoKalpha(1)). For the first time,
full profile

PDF refinements of a quasicrystal were performed: Starting
with

rational approximant models, derived from 1/1- and 2/1-Al-Mg-Zn,
its

local and medium range structure was refined (r < 27
Angstrom; R =

12.9%) using the PDF data. 85% of all atoms show Frank-Kasper
(FK) type

coordinations. The basic structural unit is the 3-shell,
104-atom

Bergman cluster (d approximate to 15 A) comprising a void
at its

center. The clusters are interconnected sharing common
edges and

hexagonal faces of the 3rd shells. The remaining space
is filled by

some glue atoms (9% of all atoms), yielding an almost
tetrahedrally

close packed structure. All Ho atoms are surrounded by
16 neighbours

(FK-polyhedron "P"). Most of them (89%) are situated in
the 2nd shell

and form a Ho-8 cube (edge length 5.4 Angstrom); they
are completed by

12 Mg atoms to a pentagon dodecahedron. Cubes in neighbouring
clusters

are tilted with respect to each other; their superposition
generates

diffraction symmetry 2/m35. The remaining Ho atoms act
as glue atoms.

As a result and as can be expected for real matter, local
atomic

coordinations in quasicrystals are similar when compared
to common

crystalline intermetallic compounds. From our results,
the long range

quasiperiodic structure of icosahedral Mg-Zn-RE (RE =
Y and some rare

earths) is anticipated to be a canonical cell tiling (CCT,
after

Henely) decorated with Bergman clusters.

Proffen, T Billinge, SJL Egami, T
Louca, D

Structural analysis of complex materials using the atomic pair

distribution function - a practical guide

ZEITSCHRIFT FUR KRISTALLOGRAPHIE 218, 2003, 132-143.

Modem materials and their properties are often characterized by varying

degrees of disorder. Routine crystallographic structure
solution only

reveals the average structure. The study of Bragg and
diffuse

scattering yields the local atomic arrangements holding
the key to

understanding increasingly complex materials. In this
paper we review

the pair distribution function technique used to unravel
the local

structure. We aim to give a practical overview and make
this method

easily accessible to the wider scientific community.

Bruhne, S Uhrig, E Gross, C Assmus,
W

Local 3D real space atomic structure of the simple icosahedral

Ho11Mg15Zn74 quasicrystal from PDF data

CRYSTAL RESEARCH AND TECHNOLOGY 38, 2003, 1023-1036.

We present a new complementary strategy to quasicrystalline structure

determination: The local atomic structure of simple icosahedral
(si)

Ho11Mg15Zn74 [a(6D) = 5.144(3)Angstrom] in a sphere of
up to r =

17Angstrom was refined using the atomic pair distribution
function

(PDF) from in-house X-ray powder diffraction data (MoKalpha(1),
Q(max)

= 13.5Angstrom(-1); R = 20.4%). The basic building block
is a 105-atom

Bergman-Cluster {Ho8Mg12Zn85}. Its center is occupied
by a Zn atom - in

contrast to a void in face centred icosahedral (fci) Ho9Mg26Zn65.
The

center is then surrounded by another 12 Zn atoms, forming
an

icosahedron (1st shell). The 2nd shell is made up of 8
Ho atoms

arranged on the vertices of a cube which in turn is completed
to a

pentagon dodecahedron by 12 Mg atoms, the dodecahedron
then being

capped by 12 Zn atoms. The 3rd shell is a distorted soccer
ball. of 60

Zn atoms, reflecting the higher Zn content of the si phase
compared to

the fci phase. In our model, 7% of all atoms are situated
in between

the clusters. The model corresponds to a hypothetical
1/1-approximant

of the icosahedral (i) phase. The local coordinations
of the single

atoms are of a much distorted Frank-Kasper type and call
to mind those

present in 0/1-Mg2Zn11.

Resonant diffraction

Attfield, JP

Multidataset refinement resonant diffraction, and magnetic structures

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND

TECHNOLOGY 109, 2004, 99-106.

The scope of Rietveld and other powder diffraction refinements

continues to expand, driven by improvements in instrumentation,

methodology and software. This will be illustrated by
examples from our

research in recent years. Multidataset refinement is now
commonplace;

the datasets may be from different detectors, e. g., in
a

time-of-flight experiment, or from separate experiments,
such as at

several x-ray energies giving resonant information. The
complementary

use of x rays and neutrons is exemplified by a recent
combined

refinement of the monoclinic superstructure of magnetite,
Fe3O4, below

the 122 K Verwey transition, which reveals evidence for
Fe2+/Fe3+

charge ordering. Powder neutron diffraction data continue
to be used

for the solution and Rietveld refinement of magnetic structures.

Time-of-flight instruments on cold neutron sources can
produce data

that have a high intensity and good resolution at high
d-spacings. Such

profiles have been used to study incommensurate magnetic
structures

such as FeAsO4 and beta-CrPO4. A multiphase, multidataset
refinement of

the phase-separated perovskite (Pr0.35Y0.07Th0.04Ca0.04Sr0.5)
MnO3 has

been used to fit three components with different crystal
and magnetic

structures at low temperatures.

Chen, JR Gu, YX Fan, HF

Solving a superstructure from two-wavelength x-ray powder diffraction

data - a simulation

CHINESE PHYSICS 12, 2003, 310-314.

Two different kinds of phase ambiguities are intrinsic in

two-wavelength x-ray powder diffraction from acentric
crystal

structures having pseudo-translation symmetry. In a test
calculation we

have solved the problem for the first time by two different
phasing

procedures developed originally in single-crystal structure
analysis.

They are the direct method of breaking enantiomorphous
phase ambiguity

in protein crystallography and that of breaking translational
phase

ambiguity for superstructures. An artificial structure
was used in the

test, which is based on atomic coordinates of the known
structure, SHAS

(C5H6O5N3K), with the atom K replaced by Rb. The arrangement
of Rb

atoms possesses a subperiodicity of t = (a + b + c)/2.
Two-wavelength

synchrotron x-ray powder diffraction data were simulated
with

lambda(1)=0.0816nm and lambda(2)=0.1319nm. Overlapped
reflections were

uniformly decomposed at the beginning and redecomposed
afterward when

the partial-structure information became available. The
enantiomorphous

phase ambiguity was resolved only for reflections with
h + k + l even.

Phases of reflections with h + k + 1 odd were derived
by the direct

method of solving superstructures. A fragment was then
obtained, which

led to the complete structure in five cycles of Fourier
iteration.

preferred orientation

Cheung, EY Harris, KDM Foxman, BM

A straightforward and effective procedure to test for preferred

orientation in polycrystalline samples prior to structure
determination

from powder diffraction data

CRYSTAL GROWTH & DESIGN 3, 2003, 705-710.

If a polycrystalline sample exhibits preferred orientation, the

relative peak intensities in the powder diffraction pattern
deviate

from the intrinsic relative diffraction intensities, and
can cause

major difficulties in attempts to determine structural
information from

the powder diffraction pattern. To circumvent this problem,
we report a

straightforward and effective test that we use routinely
as a screening

procedure to ensure that polycrystalline samples are free
of preferred

orientation before recording high quality powder diffraction
data for

use in structure determination calculations.

identification

Le Meins, JM Cranswick, LMD Le Bail, A

Results and conclusions of the internet based "Search/match round robin

2002"

POWDER DIFFRACTION 18, 2003, 106-113.

To test the effectiveness of phase identification software, a two-stage

search/match round robin using powder X-ray diffraction
data was

organized, through the internet and world wide web. The
first stage

provided powder patterns and a vague sample origin, the
second stage

provided the chemistry and sample history. While the statistics
are not

robust, it shows that routine phase identification without
chemistry

can be performed, providing effective modem third generation

search/match software is used; the most up to date databases
are

available; and well trained, experienced scientists perform
the

analysis.

Phase transition

Depmeier, W

Observation and characterization of structural phase transitions by

X-ray powder diffraction

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION 22, 2006, 367-377.

Some of the basic properties of powder diffraction are summarized after

a short introduction into the theory. Then it is described

phenomenologically how various kinds of structural transformations

affect the powder diffraction pattern. This is achieved
on emphasizing

that diffraction studies on powders are statistically
more sound than

those on single crystals, thus allowing the reliable determination
of

the generic properties of a given crystal structure.

Proteins

Von Dreele, RB Lee, PL Zhang, Y

Protein polycrystallography

ZEITSCHRIFT FUR KRISTALLOGRAPHIE Suppl 23, part 1, 2006, 3-8.

The application of powder diffraction to polycrystalline proteins has

seen a number of significant advances. Faster data collection

techniques have reduced the sample size requirement to
less than 1mg

and allowed acquisition of high quality data in < 30
s permitting in

situ exploration of protein crystallization, reactions
and radiation

damage effects. Recent developments include the formation
of heavy atom

derivatives that possibly provide a route to protein structure
solution.

Pore volumes, shapes

Kuppers, H Lieba, F Spek, AL

The determination of pore volumes, pore shapes and diffusion paths
in

microporous crystals

JOURNAL OF APPLIED CRYSTALLOGRAPHY 39, 2006, 338-346.

The original option SOLV of the program PLATON, which is primarily

devoted to the study of organic structures, has been extended
to

studies of microporous inorganic crystals. The space that
is available

for a potential spherical guest within a pore can be regarded
as being

outlined by rolling a sphere of the guest's radius over
the surfaces of

the host atoms that form the pore. The volumes of the
pores are

determined in angstrom(3) and the pore shapes can be drawn.
The pore

volumes of several microporous phases have been calculated
and compared

with results obtained with other methods. An essential
feature of the

program is the option to vary a parameter called `probe
radius', which

models the size of a guest. The decision whether a void
is a pore or

not and the dimensionality of a pore depend on the radius
of the guest,

which is approximated by a sphere. This is demonstrated
for the

structure of the zeolite afghanite. With decreasing probe
radius, cages

can coalesce into larger cages and finally into channels
and channel

systems. The variation of the probe radius allows one
to determine

whether a window between adjacent pores is permeable to
guests; in

addition, diffusion paths in zeolites and zeolite-like
structures can

be determined and visualized.

DFT

Martinez, JR Mohn, CE Stolen, S
Sondena, R

What can a "quantum black-box'' do for the inorganic thermochemist?

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 8, 2006, 2036-2039.

Enthalpies of formation of ABO(3) (A = Ca, Sr, Ba; B = Ti, Zr, Hf)
from

the binary constituent oxides have been calculated by
ab initio density

functional theory. The resulting values compare well with
the large

number of experimental determinations reported in literature.
The

trends in the calculated enthalpies of formation correlate
with the

difference in acidity between the binary constituent oxides.
Density

functional theory is shown to be a valuable tool that
should be used

routinely in thermochemical studies of inorganic compounds.

Topology

Krivovichev, S

Topology of microporous structures

MICRO- AND MESOPOROUS MINERAL PHASES

REVIEWS IN MINERALOGY & GEOCHEMISTRY 57, 2005, 17-68.

Rocha, J Lin, Z

Microporous mixed octahedral-pentahedral-tetrahedral framework silicates

MICRO- AND MESOPOROUS MINERAL PHASES

REVIEWS IN MINERALOGY & GEOCHEMISTRY 57, 2005, 173-201.

SDPD Round Robin

A. Le Bail & L. Cranswick,

SDPD Round Robin 2002 Results

IUCr Commission on Powder Diffraction Newsletter 29 (2003) 31-34.

A. Le Bail and L.M.D. Cranswick,

Revisiting the 1998 SDPD Round Robin

IUCr Commission on Powder Diffraction Newsletter 25 (2001) 7-9.

Armel Le Bail