john201004
I have two different atoms in my unit cell. One sits at 0 0 0 and other sits at 1/2 1/2 1/2, the unit cell belongs to Fm-3m. During Rietveld refinement if try to refine the atomic positions I ended up very strange structures. All atoms at corner and face center showed correct but the atom at tetrahedral site which I refined is bit weird. Instead of one atom at each tetrahedral site I ended up with four atoms which tightly packed with each other and occupied that tetrahedral sites. I don't know what is wrong? Is problem caused by my inp or there is something else?
Here is the atomic positions:
x 0 y 0 z 0
x 0.25 y 0.25 z @ 0.25
BTW, is it possible to upload and image on topas forum?
Sincerely
ahhill
I should think that you should not be refining the position of the atom at 1/4, 1/4, 1/4. It is a special position, 8c (Wyckoff). Check the crystallographic tables.
As for images, put them onto something like imageshack, then link to them with the image code.
Adrian