[Ifeffit] Breaking down correlationships between parameters

[Rana, Jatinkumar Kantilal]

Dear All,

I have stumbled upon a question regarding correlationships between various parameters in EXAFS fitting. As we know, the parameters S02*N and sigma2 are highly correlated (where N is the number of nearest neighbors).

I would like to determine the number of nearest neighbors for a series of sample subjected to some treatment. I can do this by simply setting S02 to a value for a given absorber (based on the literature or my own measurements of some reference compounds) and letting N and sigma2 vary in a fit. However, the problem is the physical process which changes the number of nearest neighbors, also introduces structural disorder in samples. Thus, I always get the values of N overestimated due to its correlationship with sigma2.

I know of a method which can be used to breakdown the correlationship between S02 and sigma2 by setting a series of S02 values at different k-weights and refining the corresponding sigma2 as discussed in several literature. However, in this approach the explicit assumption is, S02 is the property of absorbing atoms and thus is independent of changes occurring inside the sample. In my case, however, both sigma2 and N vary with changes inside samples. Is there any way to break this correlationship ?

I look forward to your valuable suggestions and comments.

Best regards,
Jatin





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