Hi Abhijeet, You can model a system with two different metal sites. You'll need to do a Feff calculation for each site separately, of course, and select the important scattering paths needed for each site. At that point you can try to fit with just one or just the other site, and see how well each does on its own. You can also set a fraction of site1 and site2 occupancy and either fix this (for example, a 2:1 ratio) or have it adjusted in the fit. To do this, simply add a parameter "frac_site1" or "x1", and use it as a multiplicative factor for the amplitudes of all the paths for site 1. For all the paths for site 2, use (1-frac_site1) or (1-x1) as a multiplicative factor for the amplitude. You can then set this parameter or allow it to be adjusted in the fit. Of course, that implies that you know a lot about the local structures of the two sites, and may need to be used with caution, but you knew that already.... --Matt On Fri, Jul 22, 2011 at 9:11 AM, Abhijeet Gaur wrote:

-- Christopher J. Patridge PhD. 405 NSC - Dept of Chemistry University at Buffalo State University of New York Buffalo, NY 14260 Office:(716)645-4137 Contact:(315)529-0501

Dear Chris,                I am sorry for making my problem a bit difficult to understand. Let me clarify the problem: 1. Yes, I have the crystal strcuture of the sample with me, from which I know that there are two metal centers. With this crystal strcuture data, I have generated the theoretical model for the two metal sites. 2. Yes, the metal centers only contain the absorbing metal, i.e., copper but with with different coordination.

    And my question is whether by using EXAFS analysis of experimetal data, the contribution of two metal center present in sample can be confirmed?     Also, is it possible to calculate that how much one metal center contribute to the experimetal data?     If, one of the theoretical model does not fit to the experimetal EXAFS data, what does it signify about the corresponding metal center?

  I hope this will make my problem clear to the members of the mailing list.

With thanks Abhijeet Gaur _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit