Re: [sdpd] Rietveld + shear planes

[Armel Le Bail <alb...@cristal.org>]

Modelizing defects in any form of matter in which there is a
random orientation (crystalline powders, amorphous solids,
liquids, gases) is better done by the Debye scattering equation.
It involves only the magnitudes of the distances r(mn) of each
atom from every other atom. Building large realistic models and
long calculations are the "only" inconvenience. Current
computers allow to do more with this approach now.

Treating directly a disorder problem with the Rietveld method
is using too many shortcuts (applying approximations generally
valuable if there is not too much departure from three-dimensional
order).

See formula (10.3) in "X-Ray Diffraction", B.E. Warren, Addison-Wesley,
1969, p. 117.

And for a software :
J. Appl. Cryst. (1993). 26, 368-383
Powerful new software for the simulation of WAXS and SAXS diagrams
D. Espinat, F. Thevenot, J. Grimoud and K. El Malki

Just my 2 EuroCents.

Best,

Armel


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