Hi, > I'm trying to fit an experimental Si pattern to refine the zero offset for > out instrument. The calculated spectrum has 2 extra lines, and three > missing lines. I've hand calculated the expected location of lines in the > experimental spectrum and account for all of the lines, so I know I don't > have the wrong spectrum or contaminated Si. [...] 2 2 0 12 0.2615814 47.5278 0.1502 3.580E+04 896. 189.198 0 0.000 not in calculated pattern 2 2 2 8 0.3203704 59.1481 0.1502 262. 7.55 16.189 0 0.000 NOT ALLOWED, but calculated 4 2 2 24 0.4530722 88.5339 0.1502 5.947E+03 150. 77.114 0 0.000 not in calculated pattern 6 2 0 24 0.5849137 128.6134 0.1502 522. 14.1 22.849 0 180.000 not in calculated pattern 6 2 2 24 0.6134627 141.8573 0.1502 166. 5.15 12.887 0 0.000 NOT ALLOWED, but calculated
I'm not a GSAS specialist but it looks like you have a spacegroup problem. If you have correctly chosen Fd-3m(227) then you still have to correctly choose the origin of the SG : it can be either Fd-3m:1 or Fd-3m:2 (I don't know how the SG origin choice is made in gsas). See the SG & origins description on the Bilbao server : http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list Practically, your Si atom should *not* be on the inversion center, which itself is either at (0,0,0) for Fd-3m:2, or at (1/8,1/8,1/8) for Fd-3m:1... It looks like you may have your si atom at (0,0,0) and are using Fd-3m:2 for a spacegroup, in which case try changing the sg origin or shift your si atom by +/-(1/8,1/8,1/8) Vincent -- Vincent Favre-Nicolin Université Joseph Fourier http://v.favrenicolin.free.fr ObjCryst & Fox : http://objcryst.sourceforge.net
