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[sdpd] (unknown)
Greetings All,
Please help me with insertion of rigid bodies in GSAS. I have been using Ian Swain's guide (for which I am very grateful) at:
http://www.ccp14.ac.uk/ccp/web-mirrors/ian-swainson/fireside_fuide_to_rigid_bodies.pdf
My difficulty is knowing the proper input to orient my rigid bodies. I chose a local cartesian coordinate system such that x//a z//axb y//(axb)xc and placed the origins at the atom which is always 0 0 0 in vector input (central atom in r.b. type 1, bent L-M-L; central atom of r.b. type 2 tetrahedral ML4) so my cartesian vectors are oriented with respect to the fractional coordinate system of the monoclinic cell (b unique). When I enter zero angles I seem to be getting a random orientation. Also why are there six rotation angles? Are these related to the six unique elements of the transformation matrix between the cartesian coordinate system and the fractional monoclinic coordinate system?
Further background on the problem. I am trying to solve a structure from powder diffraction data. I know the structure of some similar materials and have tried both EXTRA/SIRPOW and ESPOIR to generate models for refinement. I believe I have the proper fragements (this is also supported by MAS NMR data), and a roughly correct orientation in the unit cell from ESPOIR (using HKL, Fobs generated by EXTRA). I wish to try and refine the orientation of the bent and tetrahedral fragments as rigid bodies.
Roger M. Sullivan
Department of Chemistry, Box 8204
North Carolina State University
Raleigh, NC 27695-8204
Phone: 919.515.8924
FAX: 919.515.8909
smsulliv...@pams.ncsu.edu
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