[Ifeffit] Some direction

Matt Newville newville at cars.uchicago.edu
Sun Nov 23 17:00:50 CST 2003


Dear Hedy,

On Sun, 23 Nov 2003, H H wrote:

> Since, I am new in doing XAFS fitting, I hope some one
> just direct me little bit. In order to my fitting, I
> always filter each individual shell and then fit the
> back scattering. When I do that I get a good result.
> However, after I fit each individual shell and get R
> and Sigma^2, then I try to combine the shells
> together. The resultant spectrum does not match the
> fit. Do I have to combine the shells together after I
> fit each one individually or it is possible to do each
> one by its own?

I'm not sure I understand what you're doing.  Maybe you 
can be more specific?

Some questions:
- Why do you always filter each shell for fitting, as 
  opposed to fitting in R-space?   This seems much easier
  to me, and avoids many complications.  Still, fitting 
  isolated shells ought to work.

- How are you adding together the spectra from the 
  different shells after the fit?

- In what way does the sum of shells not match the fit?

--Matt



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