Dear Mathew, The 104 plane in calcite corresponds to the most intense reflection that is related, in turn, to the best "spacing" or "separation" between atomic "layers" along which the cleavage may occur. This is not a strict rule, of course, as real cleavage planes may be different depending on specific interatomic interactions in the crystal and other aspects, but it works in many cases. Note also, that the 104 plane in the hexagonal setting has several symmetry-equivalents, while most Rietveld programs normally generate only one equivalent hkl for each diffraction peak, which makes the uniaxial March-Dollase PO correction invalid for such peculiar directions. This problem is resolved in DDM, where I included a special expanded-hkl option to generate all equivalent hkl's for every peak. About other programs I'm not sure.
Best regards, Leonid ******************************************************* Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660036, Akademgorodok 50/24, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid ******************************************************* ________________________________ From: Matthew Rowles <rowle...@gmail.com> To: "Sitepu, Husinsyah" <husinsyah.sit...@aramco.com> Cc: "daniel.chateig...@ensicaen.fr" <daniel.chateig...@ensicaen.fr>; "rietveld_l@ill.fr" <rietveld_l@ill.fr> Sent: Wednesday, March 26, 2014 8:16 AM Subject: Re: PO corrections in trigonal space groups? Thanks for your replies. Husin, is there any justification for the use of the 104 direction in calcite, other than this is the direction that works? I'm all for doing it if it works, but I'd like a little theoretical backup. Thanks Daniel. I'll put something together for a look-see. What corrections are being used in Maud? Are there any papers on them? THanks Matthew
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