Dear Rietveld friends, I'm having some problems with calculating Uiso from the anisotropic parameters. Here is an example - I copy first two sites of aluminite (monoclinic):
_atom_site_aniso_label _atom_site_aniso_U_11 _atom_site_aniso_U_22 _atom_site_aniso_U_33 _atom_site_aniso_U_12 _atom_site_aniso_U_13 _atom_site_aniso_U_23 S 0.01937 0.01562 0.01277 -0.00248 -0.00027 0.00954 Al1 0.01117 0.01169 0.01295 0.00006 -0.00012 0.00789 Using the formula for Uiso for the monoclinic system, which is: 1/3 * [U22 + 1/sin^2(beta)*(U11 + U33 + 2U13cos(beta)] for the "S" site we obtain the value of 0,0054 for "Al": 0.01225 Meanwhile, the listed Uiso are: _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_U_iso_or_equiv S 0.70076 0.37376 0.93018 0.01621 Al1 0.65581 0.45332 0.47633 0.01229 While the author-given value for Al is close to the one calculated myself, the one for S is much different. By the way, 0.01621 * 1/3 = 0.0054. I could find it a simple mistake, I've found such a problem in case of many other structures. And here's my kind question: am I missing something? Best regards! -- Łukasz Kruszewski, Ph.D., adjunct Polish Academy of Sciences Institute of Geological Sciences X-Ray Diffraction Laboratory (coordinator) Twarda 51/55 str. 00-818 Warsaw Poland
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