Hi Falk, On Tue, Aug 7, 2012 at 8:42 AM, Meutzner, Falk <f.meutz...@hzdr.de> wrote: > 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 _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit