>> Why not EXPO? (Extra + Sirpow) from Team of Giacovazzo....
>> Javier
>I have been trying to solve some organic (no heavy elements) crystal
>structures from x-ray powder data (not synchrotron) but with limited
>success. The first step, after indexing, has been structure factor
>extraction via FULLPROF and then trying to get a solution with SHELX97.
>Unfortunately, SHELX isn't really designed for use with powder data and
>I rarely get a good solution. Can anyone suggest some alternative method
>which might give better results?
EXPO for Windows and UNIX is definitely the best freely available program
optimised for solving structures from powders using direct methods:
the moment to use by default.
http://www.ba.cnr.it/IRMEC/SirWare_main.html
http://www.ccp14.ac.uk/ccp/web-mirrors/sirware/IRMEC/SirWare_main.html
Tutorial run-through of it solving an organic structure at:
http://www.ccp14.ac.uk/tutorial/expo/basic.htm
Also, if using Windows, you could use the WinGX interface to
allow you friendly access to Shelxs, Dirdif and Sir92/Sir97
structure solution programs.
While the direct methods Sir and Shelx may fail - Dirdif
could succeed by using a reasonably rigid molecular fragment.
Refer:
Using WinGX with Powder Diffraction Extracted Intensities
for Structure Solution and Space Group Assignment -
http://www.ccp14.ac.uk/tutorial/wingx/powder/
---
Another option if you have a Linux or UNIX machine is to
try the CRUNCH direct methods program. It is very easy to
install and run under UNIX and has a very good reputation for
succeeding on difficult equal atom structures where others
fail (with single crystal data at least).
http://www.ccp14.ac.uk/tutorial/crunch/
With Platon for UNIX, there is also a "System S" that is a
structure solution and refinement suite which links in
Shelxs, Sir97, Dirdif and Crunch (pretty much like WinGX
does for Windows)
http://www.ccp14.ac.uk/tutorial/platon/
(The links betwee System S to the latest Dirdif and Crunch are
temporarily broken (but will hopefully be fixed soon) in the
next releases of the software.
I guess one of the "last resort" options would be to try
one of the direct space programs such as ESPOIR which
Armel was demonstrating at the IUCr Congress in Glasgow:
http://fluo.univ-lemans.fr:8001/sdpd/espoir/
http://www.ccp14.ac.uk/ccp/web-mirrors/armel/sdpd/espoir/
Lachlan.
--
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: [EMAIL PROTECTED] Ext: 3703 Room C14
http://www.ccp14.ac.uk
