Dear FullProf users, I would like to make a pcr file for a Heusler alloy with so-called A2 structure, in which three atoms are completely disordered. (See Fig.1 in http://dx.doi.org/10.1088/0022-3727/48/16/164011 or this direct link http://cdn.iopscience.com/images/0022-3727/48/16/164011/Full/jphysd500490f01_online.jpg)
For example, a straightforward description of A2 Heusler alloy Co2FeSi would be like this. I m -3 m <--Space group symbol !Atom Typ X Y Z Biso Occ In Fin N_t Spc /Codes Co Co 0.00000 0.00000 0.00000 0.50000 0.01041 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Fe FE 0.00000 0.00000 0.00000 0.50000 0.00521 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Si SI 0.00000 0.00000 0.00000 0.50000 0.00521 0 0 0 0 0.00 0.00 0.00 0.00 0.00 (general multiplicity = 96, multiplicity of (0,0,0) is 2, so Occ=0.02083 when fully occupied by one atom) But, as many of you know, FullProf assumes that "THE FIRST GIVEN SITE IS FULLY OCCUPIED OR THE FIRST AND SECOND ATOMS ARE IN THE SAME SITE WITH TOTAL FULL OCCUPATION (If this is not the case, change the order of atoms to obtain correct values for the content of the unit cell)” (quoted from a output file). Accordingly, a cif file generated after running of a pcr with the atomic position above shows unintended values as below. loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_U_iso_or_equiv _atom_site_occupancy _atom_site_adp_type # Not in version 2.0.1 _atom_site_type_symbol Co 0.00000 0.00000 0.00000 0.00633 0.66645 Uiso Co Fe 0.00000 0.00000 0.00000 0.00633 0.33355 Uiso Fe Si 0.00000 0.00000 0.00000 0.00633 0.33355 Uiso Si This rule seems tricky if one wants to make an unit cell consisting of sites occupied by multiple atoms like A2-type Heusler alloys. Actually, I came up with an idea to place a “transparent” dummy atom using Nsc option at the top of the atomic position list to bypass the rule, and it seems to work. But I’m not sure this is the best way. Does anyone have other or better ideas? Thanks in advance. Kotaro //================//================// Kotaro SAITO High Energy Accelerator Research Organization Institute of Materials Structure Science 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan //================//================//
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