There is a new GSAS tutorial on the CCP14 site:
Setting up GSAS Macro Files for Restrained Refinement on relatively
large Inorganics (Polymeric Inorganics) (using a "created" Ti Fe O
example - originally just a new published Titanate phase)
http://www.ccp14.ac.uk/solution/gsas/restrained_inorganic.html
This deals with:
i) atom co-ordinates macro file
ii) atom bond length restraints macro file (generated from Crystals
with the option of performing DLS - and Scott Belmonte's new
"coue" conversion software)
iii) dual atom occupancy constraints for the metal sites
iv) total cell contents restraints macro file
Corrections, suggestions, etc appreciated. Especially new macros for
making this type of thing easier to set up for certain types of
restraints where it is important to test the robustness from different
starting positions and refinement strategies.
Lachlan.
PS: While GSAS scales very well in terms of increased problem size and
interface control - I am having some difficulty with getting convergence
within Genles on a "real" dataset. (this is on Le Bail fitted data where
only the background and atomic parameters are allowed to refine - starting
from an idealised starting model guided from TEM)
Does anyone have hints and tricks for parameter release conditions for
large inorganics (that required restraints to keep the Oxygen distances
reasonable) (~100 atoms in the asymmetric unit - may have to be doubled
based on reinterpretation of the TEM data). All the metal sites have
potential dual occupancy with that can be varied. What can you get away
with and have a good change of convergence with Genles? How far away from
their true positions can the heavy atoms be to drop in? Estimates of
a good numbers of cycles to use to let the atoms rattle around?
Are there possibilities for what I believe on the commercial(?) version
of Shelx 76(?) was a "cascading" refinement(?) - to automatically
release small sets of atoms - and cycle through automatically?
(is it possible to interlink expedt and genles under macro control
to achieve this?)
--
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
