Re: Extracting Structure Factors

Armel Le Bail ( armel@fluo.univ-lemans.fr )
Fri, 20 Dec 1996 16:37:57 +0100

At 08:59 20/12/1996 EST, Bill Beer wrote:
>...
>I have been trying to use GSAS, with limited success, by
>placing a dummy atom at a non-special position for the
>Le Bail extraction. The discussion has suggested that other
>programs implement the Le Bail method in different, possibly
>better, ways. Is FULLPROF the 'preferred' choice? I have
>found that program on the Web page, but if there are other
>programs, I would appreciate reference to PC versions. In
>March '95, a citation list of Rietveld related programs was
>distributed by Le Bail. This includes several that are
>'Pawley method' based. None of these programs seem to be
>listed on the Web page. Is there a reference that describes
>the relative advantages of the Pawley and Le Bail methods for
>extracting structure factor amplitudes?

C. Giacovazzo presented a comparison at the XVII IUCr Congress
but the summary is not as explicit as was the conference:
http://www.bmsc.washington.edu/iucr/abstracts/abstracts/E0451.html
I have retained from this conference 2 pictures showing potential holes:
several holes for the Pawley method and only one hole for mine. Thanks
Mr. Giacovazzo :-).

Actually, the most complete paper seems to be 'Direct methods and
powder data : state of the art and perspectives', C. Giacovazzo, Acta
Crystallogr. A52 (1996) 331-339. Inside is a comparison of the Pawley
and Le Bail methods through respectively the ALLHKL and EXTRA
softwares.

For a list of all programs used for structure factor extraction, see :
http://fluo.univ-lemans.fr:8001/iniref/progmeth.html#n2
this file is a part of the Structure Determination from Powder Diffraction
Database (SDPD-D) at http://fluo.univ-lemans.fr:8001/iniref.html

I do not know if FULLPROF is the best choice. I can just say that it
is really efficient and easy to use (with experience). I have used GSAS
too and know MPROFIL5 (distributed by CCP14) in which the
method implementation was directly obtained from my own software
ARITB (both had the same Thomas and Bendall multipattern version
basis) by A. Jouanneaux. I have not tried the other possibilities as
EXTRACT, EXTRA (PC available), PROFIL(?), and some unnamed softwares, nor
all the Pawley-based programs with the exception of
ALLHKL.

Merry Christmas, and solve your structure,

Armel