[sdpd] Re: indexing superstructures

[L.M.D.Cranswick... @dl.ac.uk (L. Cranswick)]

> I would like to know if exists a software devoted to the indexation of
> superstructure lines in a powder pattern.
> 
> i.e. : I have a powder pattern and managed to index (by analogy with a known
> structure) the majority of the lines. I have some remaining unindexed lines
> and am pretty sure that they do not belong to an additional phase.
>         I wonder if exists some software taking into account (contrary to
> the usual indexation programs like dicvol, treor) the cell already indexed
> and trying to index the remaining lines in a supercell automatically.
> 

Has you tried the following:
  Program: SUPERCELL  (J.Rodriguez-Carvajal, LLB-December-1998)

"This program can be used to index superstructure reflections from
  a powder diffraction pattern. The program needs "nobs" observations
  (angular positions of satellite peaks) to work. The variable nobs is
  limited to a maximum of 40."
FIRST APPROACH
  The first approach consist in searching the best "unit cell"
  compatible with a set of SUPERSTRUCTURE observed lines in powder
  diffraction.
SECOND APPROACH
  If the first approach fails to give a suitable solution the superstructure
  may be inconmensurate and a direct search for the propagation vector and
  one of its harmonics have to be used.

This is downloadable off the original French site and mirrors.

This comes with the Winplotr software for Windows
  http://www-llb.cea.fr/winplotr/winplotr.htm
  http://www.ccp14.ac.uk/ccp/web-mirrors/plotr/winplotr/winplotr.htm
  ftp://ftp.minerals.csiro.au/pub/xtallography/ccp14/ccp/web-mirrors/plotr/plotr/plotr.htm

  ftp://bali.saclay.cea.fr/pub/divers/winplotr/
  http://www.ccp14.ac.uk/ccp/ccp14/ftp-mirror/fullprof/pub/divers/winplotr/
  ftp://ftp.minerals.csiro.au/pub/xtallography/ccp14/ccp/ccp14/ftp-mirror/fullprof/pub/divers/winplotr/

---

Another option is to use Brian Toby's CMPR software for
manual indexing which I am told is very nifty in this
area.  I have only used it myself with trivial
cells.  As you have a cell of sorts, you can then
interactively use slide bars to be visually trying to
sort out the reflections without the nuances of the
automated programs(?).

Refer:
  http://www.ccp14.ac.uk/tutorial/cmpr/index.html

Lachlan.

> 
> ---------------------------------------------------------------
> Jean-Marc Joubert
> Laboratoire de Chimie Metallurgique des Terres Rares
> CNRS -  UPR 209
> 2-8 rue Henri DUNANT,
> 94320 THIAIS CEDEX - FRANCE
> 
> Phone:	33 (0)1 49 78 12 11
> Fax:   	33 (0)1 49 78 12 03
> 
> Email: 	joubert... @glvt-cnrs.fr


-- 
Lachlan M. D. Cranswick

Collaborative Computational Project No 14 (CCP14)
    for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick... @dl.ac.uk  Ext: 3703  Room C14
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