Hi Falk,
On Tue, Aug 7, 2012 at 8:42 AM, Meutzner, Falk
Dear IFEFFIT Community,
is there a way to calculate the spectrum for chemically disordered systems? We have a simple binary bcc structure. It crystallises either in superstructure (CsCl) or chemically disordered (W type) with both atoms randomly taking part of either (0,0,0) or (0.5,0.5,0.5). It is easy to get the superstructured model for artemis, but we have no clue how to model the disordered system...
Thanks a lot for your help, we really appreciate it.
Best regards Falk
Feff generates the EXAFS contributions for an individual atom in a cluster of atoms. To model a range of local structures that an atomic species might have in a disordered (or even moderately complex ordered structure, such as two inequivalent sites in a unit cell), one has to do a calculation for each candidate environment for the absorbing species and average the results accordingly. To model the disordered system, I think you would need to run one calculation with the central atom at the (0, 0, 0) site and one at the (1/2, 1/2, 1/2) site. You can then add the weighted contributions from the corresponding paths from each calculation. One of the things EXAFS might be able to distinguish (depending on the Z contrast of the atoms in your structure) is whether one site is preferred over another. I hope that helps get you started. If not, perhaps a more concrete question would help. --Matt