>
> Dear INEL users
> All I can tell you is that I've found that ZERO makes a
>better job of picking up all the vertical shifts and zero errors etc
>than 'shft' in fact when I try using 'shft' the refinements often
>become unstable. The probable reason for this is using the BB
>model on reflection geometry. Perhaps I should have put this in my
>last message.
> Yours
> Rory.
Acctualy, it does not matter what do you refine if you use only
low angle part of pattern (~<60-70 deg 2theta). Either of them
is OK: ZERO shift, sample shift or even beam penetraiting in case
of low absorption. BUT if you do not know exactly what cases you
peaks shift, your cell is incorrect. However, if you use modern
diffractometer (good aligned, of course) ZERO shift is 0 or very
close to it and if sample absorb X-ray very well everything that
left is SAMPLE shift that has to be refined and I never found it
unstable. The best thing to do is to use full pattern at least to 120
deg 2theta and refine all 3 parameters -- they do not correlate!
One could simply draw graph and see their dependence on 2theta
is quite different but, again, only in the full or almost full range.
Peter.