[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [sdpd] Just press the button
Hi,
Finally, we can wait a bit before closing this SDPD
mailing list. It seems that in some cases, just pressing
the EXPO2004 button will not be enough ;-) The paper
conclusion is : "A high level of automation has been secured
(the program evaluates the quantity of information available
at each critical point and makes its own choices), but the user
can apply special strategies when the solution is not attained
by the default run".
OK, let us continue to talk about those special strategies
in SDPD... though the mailing list is rather silent in spite
of all these manuscripts (and books) published on the subject.
EXPO2004 seems now to have phagocytozed almost every
innovation proposed in SDPD during the last 20 years. Most
of these innovations were said to be even improved all along the
publication of an impressive list of papers (mainly authored
by Altomare et al., see below). Hard to compete with this
big team occupying every place in the structure solution topic
(single crystal as well as powder), like in a GO game party.
Union makes the strength. A kind of Powder Dream Team,
working in alphabetical order, winning regularly medals.
Impressive. Congratulations.
I recognize being unable (and in fact not wanting) to install
any equivalent dream team in the french research system.
Armel
PS - Main list of papers in the long story of SIRPOW/EXPO,
classified by times cited (TC) :
------------------------------------------------------------------------
TC=192
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 28 (1995) 842-846.
Extraction of structure-factor amplitudes from a powder diffraction
pattern is not a straightforward procedure. Peak overlapping and
background estimation are the main obstacles to the process: they may
introduce strong correlations among reflection intensities and heavy
errors in their estimates. The program EXTRA is described, which, on the
basis of the Le Bail algorithm, is able reliably to estimate the
structure-factor amplitudes in a fully automatic way.
------------------------------------------------------------------------
TC=141
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 32 (1999) 339-340.
EXPO is the integration of two programs, EXTRA and SIRPOW.92, the
first devoted to full powder pattern decomposition and the second to the
solution and refinement of crystal structures. The program is able to
exploit the prior information obtained during the crystal structure
solution process for improving the classical decomposition. EXPO also
allows preliminary cycles of Rietveld refinement.
------------------------------------------------------------------------
TC=61
ALTOMARE, A CASCARANO, G GIACOVAZZO, C GUAGLIARDI, A
EARLY FINDING OF PREFERRED ORIENTATION - A NEW METHOD
JOURNAL OF APPLIED CRYSTALLOGRAPHY 27 (1994) 1045-1050.
Pattern decomposition programs are able to derive, from the measured
powder diffraction patterns, estimates of the square moduli of the
structure factors. A method is described that, by statistical analysis
of the normalized structure-factor moduli, is able to obtain information
about the possible presence of preferred orientation. Cylindrical
symmetry of the specimen is necessary. The method proves to be efficient
and quite useful for the application of direct methods to powder data.
------------------------------------------------------------------------
TC=58
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 vertical bar F vertical bar's
JOURNAL OF APPLIED CRYSTALLOGRAPHY 31 (1998) 74-77.
The positivity of the Patterson function is used as prior information
for the decomposition of a powder diffraction pattern. An automatic
procedure is described which, integrated with the Le Bail method, is
able to provide estimates of \F\ values that are often remarkably better
than those obtained by application of standard techniques. The
procedure, implemented in a computer program, has been applied to a set
of test structures (experimental data); the results show that,
particularly for structures with some heavy atoms, the new estimates of
the structure-factor moduli are far better (on average) than those
obtained via the default application of EXTRA [Altomare et nl. (1995).
J. Appl. Cryst. 28, 842-846].
------------------------------------------------------------------------
TC=30
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 28 (1995) 738-744.
When in a powder diffraction pattern two or more peaks heavily
overlap, the integrated intensities of the overlapping reflections are
correlated. This paper describes a method, based on the study of the
peak overlap, which estimates the number of statistically independent
intensities associated with a powder diagram. Such a number can be
useful for forecasting the rate of success of direct-methods procedures
for ab initio crystal structure solution and for evaluating a priori the
efficiency of least-squares programs devoted to crystal structure
refinement.
------------------------------------------------------------------------
TC=17
Altomare, A Giacovazzo, C Guagliardi, A Moliterni, AGG Rizzi, R Werner, PE
New techniques for indexing: N-TREOR in EXPO
JOURNAL OF APPLIED CRYSTALLOGRAPHY 33 (2000) 1180-1186.
Indexing of a powder diffraction pattern is still a critical point in
procedures aiming at solving crystal structures from powder data. New
code has been associated to the program TREOR90 in order to define an
efficient peak search procedure, to modify the crystallographic
decisions coded into TREOR90 to make it more exhaustive, to refine the
selected unit cell automatically, and to make the entire procedure user
friendly, via a graphical interface. The new program, called N-TREOR,
has been integrated into the package EXPO to create a suite of programs
able to provide a structural model from the analysis of the experimental
pattern. N-TREOR is also available as a stand-alone program.
------------------------------------------------------------------------
TC=12
Altomare, A Foadi, J Giacovazzo, C Guagliardi, A Moliterni, AGG
Solving crystal structures from powder data .2. Pseudotranslational
symmetry and powder-pattern decomposition
JOURNAL OF APPLIED CRYSTALLOGRAPHY 29 (1996) 674-681.
Pseudotranslational symmetry may be characterized by the performance
of statistical calculations on the normalized structure factors. The
efficiency of the method is quite high if single-crystal data are used.
When only powder data are available, the characterization process is not
straightforward; in this paper, it is shown how it can safely be done.
The information so gained may be used as prior information in the
pattern-decomposition process. It is shown that its use improves the
estimates of the integrated intensities, with consequent benefit for the
efficiency of the direct phasing process.
------------------------------------------------------------------------
TC=10
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.
The principal limitation of the diffraction methods for crystal
structure analysis from powder data is originated by the collapse of the
three-dimensional reciprocal space into the one dimension of the powder
diffraction pattern. The degradation of the information can make
difficult even the solution of small crystal structures and can generate
inefficiencies in the least-squares methods devoted to crystal structure
refinement. In this paper, the current two-stage procedures, the first
stage dedicated to powder-pattern decomposition and the second to direct
phasing of powder data, are analysed. It is shown that in the first
stage such procedures disregard a large amount of information that can
become available during the process of crystal structure solution and
analysis. The use of such information is essential for making
direct-methods procedures more robust and for improving the accuracy of
the least-squares techniques. The performances of EXTRA [Altomare,
Burla, Cascarano, Giacovazzo, Guagliardi, Moliterni & Polidori (1995).
J. Appl. Cryst. 28, 842-846], a program for full-pattern decomposition
based on the Le Bail algorithm, and of SIRPOW.92 [Altomare, Burla,
Cascarano, Giacovazzo, Guagliardi, Polidori & Camalli (1994). J. Appl.
Cryst. 27, 435-436], a direct-methods program optimized for powder data,
are discussed in order to offer to the reader a logical pathway for the
analysis of the traditional techniques and for the proposition of a new
approach. It is shown that pattern-decomposition programs based on the
Le Bail algorithm are able to exploit the prior information in a more
effective way than Pawley-method-based decomposition programs.
------------------------------------------------------------------------
TC=10
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.
A recent statistical method for deriving information about the
presence of a preferred orientation plane [Altomare, Cascarano,
Giacovazzo & Guagliardi (1994). J. Appl. Cryst. 27, 1045-1050] has been
revisited. Some implications of the method are theoretically discussed.
The method is applied to various practical cases in order to give
insight into its potential and its limits and into the correlation
between its indications and full-pattern decomposition programs, peak
overlapping and data resolution.
------------------------------------------------------------------------
TC=7
Altomare, A Burla, MC Giacovazzo, C Guagliardi, A Moliterni, AGG
Polidori, G Rizzi, R
Quanto: a Rietveld program for quantitative phase analysis of
polycrystalline mixtures
JOURNAL OF APPLIED CRYSTALLOGRAPHY 34 (2001) 392-397.
Quantitative determination of phase abundance in a multicomponent
polycrystalline mixture is a basic goal in materials characterization.
Because of several advantages compared with traditional techniques, the
Rietveld method has been increasingly applied to this task. Further
progress in this direction would be to carry out the analysis
automatically. The new Rietveld package Quanto is devoted to the
automatic estimation of the weight fraction of each crystalline phase in
a mixture. The amorphous content can be estimated by means of the
internal-standard method. Corrections for preferred orientation and
microabsorption effects are available. A user-friendly graphical
interface facilitates interaction. A data bank including several organic
and inorganic phases is supplied with the program.
------------------------------------------------------------------------
TC=7
Massarotti, V Capsoni, D Bini, M Altomare, A Moliterni, AGG
Ab initio structural approach on polycrystalline Y2-xCaxBaNiO5 (0 <=
x <= 0.33) compounds
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 214 (1999) 205-210.
The procedure of ab initio structure solution from conventional X-ray
powder diffraction data is successfully applied to a series of
Y2-xCaxBaNiO5 compounds (0 less than or equal to x less than or equal to
0.33). The study aimed at understanding if the presence of dopants in
polycrystalline Y2BaNiO5 compound can influence the success of the
structure determination process and at quantifying: the substitutional
defect. The new code EXPO has been used to obtain the most accurate set
of structure factor moduli and to perform the direct methods procedure.
It is demonstrated that the substitution on a crystallographic site, as
for the above mentioned compound, does not compromise the performance of
direct methods. The structural parameters obtained for samples with
different x values are compared with those reported in the literature.
It is pointed out that the knowledge of the dependence of lattice
parameter and cell volume values on the cation site occupancy factors
allows the direct determination of the degree of substitution of calcium
on yttrium site of the sample.
------------------------------------------------------------------------
TC=6
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 33 (2000) 1305-1310.
Direct methods applied to powder diffraction data often provide well
located heavy atoms and unreliable light-atom positions. The completion
of the crystal structure is then not always straightforward and may
require a considerable amount of user intervention. The heavy-atom
connectivity provided by the trial solution may be used to guess the
nature of the coordination polyhedra. A Monte Carlo procedure is
described which, in the absence of a well defined structural model, is
able to locate the light atoms correctly under the restraints of the
experimental heavy-atom connectivity model. The correctness of the final
model is assessed by criteria based on the agreement between the whole
experimental diffraction pattern and the calculated one. The procedure
requires little CPU computing time and has been implemented as a routine
of EXPO [Altomare et al. (1999). J. Appl. Cryst. 32, 339-340]. The
method has proved to be sufficiently robust against the distortion of
the coordination polyhedra and has been successfully applied to some
test structures.
------------------------------------------------------------------------
TC=5
Altomare, A Burla, MC Camalli, M Carrozzini, B Cascarano, G
Giacovazzo, C Guagliardi, A Moliterni, AGG Polidori, G Rizzi, R
Toward EXPO: From the powder pattern to the crystal structure
EPDIC 5, PTS 1 AND 2 MATERIALS SCIENCE FORUM 278-2 (1998) 284-288.
Recently devised techniques for powder pattern decomposition will be
discussed: they exploit the supplementary information available during
the phasing process, so improving by far the pattern decomposition and
the crystal structure solution process. A new package, EXPO, integrates
EXTRA [1], a Le Bail-based [2] full pattern decomposition program, with
a new version of SIRPOW.92 [3], a direct methods package optimized for
powder data. Different ways of combining various kinds of structural
information will be discussed and some applications to test structures
will be presented.
------------------------------------------------------------------------
TC=4
Altomare, A Giacovazzo, C Moliterni, AGG Rizzi, R
A random procedure for the decomposition of a powder pattern in EXPO
JOURNAL OF APPLIED CRYSTALLOGRAPHY 34 (2001) 704-709.
AB The main obstacle to ab initio crystal structure solution by powder
data is the lack of accuracy in the single Bragg integrated intensity
estimates. The two-stage method proves powerful for solving crystal
structures from powder data: in the first stage, the integrated
intensities and, consequently, the structure-factor moduli, are
extracted from the pattern for each reflection; in the second stage,
direct methods may be applied to estimate the phases of the structure
factors. The greater the accuracy of the integrated intensities, the
more efficient the phasing procedure. A new procedure is described,
aiming at overcoming the tendency of the Le Bail algorithm [Le Bail et
al. (1988). Mater. Res. Bull. 23, 447-452] to equipartition the
intensities of strongly overlapping reflections. It proves to be
efficient for lowering the phase error in the phasing process. The
procedure has been implemented in the EXPO program [Altomare et al.
(1999). J. Appl. Cryst. 32, 339-340].
------------------------------------------------------------------------
TC=4
Altomare, A Giacovazzo, C Guagliardi, A Moliterni, AGG Rizzi, R
Solving crystal structures from powder data. V. Located molecular
fragment and powder-pattern decomposition
JOURNAL OF APPLIED CRYSTALLOGRAPHY 32 (1999) 963-967.
AB In direct procedures for crystal structure solution from powder data,
information on the location and orientation of a molecular fragment may
readily become available. Such information may be used retrospectively
to improve the powder-pattern decomposition, with favourable effects on
the phasing process. A method is described by which accurate estimation
of a large number of structure-factor moduli is possible by exploiting
the prior partial structural information.
------------------------------------------------------------------------
TC=3
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.
------------------------------------------------------------------------
TC=2
Altomare, A Caliandro, R Giacovazzo, C Moliterni, AGG Rizzi, R
TI Solution of organic crystal structures from powder diffraction by
combining simulated annealing and direct methods
SO JOURNAL OF APPLIED CRYSTALLOGRAPHY 36 (2003) 230-238.
AB 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.
------------------------------------------------------------------------
TC=2
Massarotti, V Capsoni, D Bini, M Altomare, A Moliterni, AGG
X-ray powder diffraction ab initio structure solution of materials
from solid state synthesis: the copper oxide case
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 213 (1998) 259-265.
The results of an ab initio structure determination of a series of
CuO powder samples are reported. It is shown that the thermal treatment
affects the peak broadening and overlapping and determines the
possibility to get the cell size and the atomic positions. It is also
demonstrated that the highest level of sintering not always assures the
best results in the ab initio procedure as can be seen from the CuO
sample prepared at 1273 K. This study suggests that, when possible, it
is better to apply the nb initio procedure to a series of samples
differently annealed than to use directly the highest sintered powder.
------------------------------------------------------------------------
TC=1
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.
------------------------------------------------------------------------
TC=1
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.
------------------------------------------------------------------------
TC=1
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 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 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 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.
------------------------------------------------------------------------
Massarotti, V Capsoni, D Bini, M Altomare, A Moliterni, AGG
X-ray diffraction study of polycrystalline Y2BaO4: a test of the new
EXPO program
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 214 (1999) 200-204.
In order to test the new EXPO program, an ab initio structure
determination from conventional X-ray powder diffraction data has been
performed on Y2BaO4. a stable compound that can form during the
synthesis of mixed oxides belonging to the Y-Ba-Cu-O and Y-Ba-Ni-O systems.
An orthorhombic cell (Pnma space group) with a = 10.3955(1) Angstrom,
b=3A503(1) Angstrom, c=12.1157(1) Angstrom. Z =1 and D-c = 5.795 g/cm(3)
has been obtained, in agreement with the hypothesis that Y2BaO4 is
isotypic with Y2SrO4, as reported by Costa Ferretti. Fornasini,
Franceschi, Olcese, 1989. The: Pnca space group (60) related to the Pnab
proposed by Kwestroo, van Hal, Langereis, 1974 can be rejected.
On the basis of accurate atomic fractional coordinates determined by
direct methods application and Rietveld refinement, bond lengths and
angles have been estimated and discussed with respect to the data of the
isotypic Y2SrO4 structure.
------------------------------------------------------------------------
Altomare, A Giacovazzo, C Guagliardi, A Moliterni, AGG
Solving crystal structures from powder data: The use of a molecular
fragment
EPDIC 5, PTS 1 AND 2 MATERIALS SCIENCE FORUM 278-2 (1998) 289-293.
The problem of recovering the complete structure from a partial one,
defined via the application of direct methods to powder diffraction
data, will be analysed. A new method able to improve the structure
factor moduli estimates, exploiting the knowledge about a known and well
oriented fragment, will be described. This procedure works integrating
the results by EXTRA [1], a Le Bail-based [2] full pattern decomposition
program, and the information by a new version of SIRPOW.92 [3], a direct
methods package optimized for powder data.
Some applications to practical cases will be shown.
------------------------ Yahoo! Groups Sponsor --------------------~-->
Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar.
Now with Pop-Up Blocker. Get it for free!
http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/UIYolB/TM
--------------------------------------------------------------------~->
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/sdpd/
<*> To unsubscribe from this group, send an email to:
sdpd-unsubscribe...@yahoogroups.com
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/