You may be lucky enough that bond distance and angle constraints will
be sufficient for your purposes. Do not be afraid to weight them very
highly, so that they will have significant leverage on the
refinement. If your cation is complex, the constraints may not be
enough to keep the geometry reasonable. In that case, rigid bodies
are the way to go, but they can be quite complex to set up,
particularly if you want to allow some internal degrees of freedom.
Here are links to two tutorials on rigid bodies, from Robert
Dinnebier and Ian Swainson:
http://www.uni-bayreuth.de/departments/crystal/rietveld/rigid_bodies.pdf
http://www.ccp14.ac.uk/ccp/web-mirrors/ian-swainson/
fireside_fuide_to_rigid_bodies.pdf
Brian
On Dec 11, 2007, at 3:19 PM, Ramadas Sunil Pophale wrote:
Dear friends,
I am new to the community and had a question for GSAS users.
I have a powder diffraction data for a zeolite + template (organic
molecule) system. I would like to know the best way to represent the
molecule for refinement purposes. I currently include it as part of a
phase along with the Si and O atoms and set soft constraints on the
bond
lengths. I wonder if this approach is good enough or should I try the
rigid unit option (which does not look trivial, any good link
discussing
this option?)
Thanks for your help.
Regards,
Ramdas Pophale.
********************************************************************
Brian H. Toby, Ph.D. office: 630-252-5488
Materials Characterization Group Leader, Advanced Photon Source
9700 S. Cass Ave, Bldg. 433/D003 work cell: 630-327-8426
Argonne National Laboratory secretary (Marija): 630-252-5453
Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov
********************************************************************
