[EMAIL PROTECTED] wrote: > > Dear All, > > I am trying to do Rietveld refinement of Zirconium using GSAS. Its space > group is p 63/mmc (194). It is a hexagonal closed packed system with two atoms > per unit cell. Position of the one atom is (0, 0, 0) and that of the other is > (2/3, 1/3, 1/2). > > I am also giving the atom coordinates i.e. x,y,z as (0, 0, 0) for Zr1 and > (0.666, 0.333, 0.5) for ZR2 in GSAS. > > I think I am doing wrong because it is giving very bad result.. > > Please suggest what should I give as the atom coordinates. > > Thanking you all. > > Regards, > > Apu > > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ > Apu Sarkar > Research Fellow > Variable Energy Cyclotron Centre > Kolkata 700 064 > phone: 91-33-2337-1230 (extn. 3190) > Fax: 91-33-2334-6871 > INDIA > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
I personally would use 2/3, 1/3, 1/2 for the Zr2 coordinates. With out digging into the code I do not know if the 0.666 is recognized as 2/3. If you must use the decimal fraction, at least use 0.667 or 0.6667. The GSAS code used to recognize fractions and convert them properly and that would guarantee proper values for the coordinates. Also since the space group listed in the literature is P6/mmc, you might have better luck with a change of space groups. The 63 translation is placing both Zr1 and Zr2 at z=0 and at z=1/2. Allen Larson
