I would make a feff.inp file corresponding to the Co as a central atom in CoGa
in its original CsCl structure. Then, I would substitute all Ga atoms by Co
(the two sites are crystallographically equivalent in the bcc lattice, and
there is no need to do it separately for Cs and Cl sites). That
Since in your case it is not a random alloy (I just realized that Co does not
substitute for Ga, only Ga for Co, and thus this material should have
compensating vacancies on Ga sites), you should include the possibility of
vacancy in your fitting scheme.
For the first neighbors it will be:
