You should modify feff.inp by hand. No automatic procedure generating a single cluster that will be characterized by statistical RDF of AB, AA and BB correlations exists and here is why. In any individual cluster the radial distribution of neighbors Rho_{AB}(r)= dN_{AB}/dr, where dN is the number of A-B bonds in interval dr, is not representative of an ensemble since the requirement that the number of B type neighbors to the A type atom in each "shell" is equal to the bulk concentration of B can be satisfied only for the central A atom (that has coordinates 0,0,0). There is an interesting procedure of simulating a random alloy cluster that was published by J. Moonen, J. Slot, L. Lefferts, D. Bazin, H. Dexpert in Physica B, 208 & 209 (1995) 689-690. They populate the cluster 5000 times, truly randomizing the "average" cluster, but each of their individual clusters has RDF deviating from the average. It is besides the point though that to simulate the EXAFS of an alloy it may not be important to generate such a statistically random cluster because the single scattering or multiple-scattering paths {A<->NN<-->NN<-->A) depend only on the types of neighbors in the linkages and not so much on the surrounding. It is due to the transferability of photoelectron amplitude and phase that makes it not too sensitive. Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Mauro Rovezzi Sent: Sunday, November 13, 2005 5:19 PM To: IFEFFIT Subject: [Ifeffit] atoms and the alloys Hi to all, I have noticed that Atoms fails to generate a correct "feff.inp" file in the case of alloys. For example, let's take the Ni_xCu_{1-x}, x=0.5, an fcc substitutional. If I put Ni as central atom and give 0.5 occupancy on the shared Cu-Ni site (0,0,0.5) the result is a normal Ni fcc without Cu. At the moment I modify my feff.inp by hand to simulate alloys, but maybe I'm just not using Atoms properly. If this is the case, it could be useful to insert your answer in the FAQ. Cheers, Mauro _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit