[Ifeffit] Structures with multiple crystallographic sites

Vadim G Palshin vpalshi at lsu.edu
Thu Apr 19 22:14:03 CDT 2007

>Do a Feff calculation with each unique Co site as the absorbing atom,
>then use paths from each calculation, weighted by the fractional site

Thanks, Matt! Yes, that's exactly what I tried doing. It's a simple cubic lattice with 
20 atoms per unit cell, 8 of one type (Co1) and 12 of the other (Co2). So I did two 
FEFF runs in the same Artemis project, with Co1 and Co2 as the core atom, and 
multiplied their respective amplitudes by 0.4 and 0.6. Then I noticed that if I calculate
a sum of all included paths I get a different FT spectrum than if the sums are calculated
separately for the two FEFF runs and averaged (with correct weighting) outside of 
Artemis. Of course, it is a bit late here and I could be missing some obvious mistake.
On the other hand, I am trying for 1.6-5.5 angstrom fitting range, which involves 70+ 
paths for Co1 core and ~120 for Co2. Is it possible that Artemis does not like to deal 
with too many paths and/or variables? I better go check the manual... :o)
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