[Ifeffit] [howto] configurational average in EXAFS with FEFF

Mauro Rovezzi rovezzi at esrf.fr
Wed Mar 28 11:59:12 CDT 2007

Bruce Ravel wrote:
> If I understand what you are trying to do, this paper by me might be
> relevant: 
>  Role of local disorder in the dielectric response of BaTaO2N,
>  B. Ravel, Y-I. Kim, P.M. Woodward, and C.M. Fang, Physical Review B,
>  73, p. 184121 (2006)
> I used a DFT result as the basis of my fitting model in that paper.
> The naive approach was to make a Feff path from every absorber/
> scatterer pair in the box.  That's certainly a good idea, but Ifeffit
> has some compiled-in limitations that made that impractical.  My
> solution was to make an evenly spaced grid in R and bin together paths
> with similar path lengths.  That reduced the problem to a tractable
> number of Feff paths at the expense of writing a one-off program as a
> processing step between the DFT and setting up the EXAFS fit.
> If my answer is relevant to your problem, I have a few other ideas
> about how to approach the problem that we can discuss futher, if
> you'd like.


Your article is exactly what I was searching for. Also in my case I have
to take into account the local disorder found by DFT calculations and
the idea to bin together paths with similar length is what I supposed
but I had difficulties to realize it in practice.

What I have done is to plot a pair radial distribution function and find
out averaged distances to put in a FEFF calculation. Reading your
article seems to me that you have done this average-step after a full
calculation of paths, isn't it?

It would be great to discuss further this subject and also to open the
discussion on how to introduce some EXAFS-knowledge in DFT calculations,
as you write in the last paragraph of the article.


Mauro Rovezzi <rovezzi at esrf.fr>
PhD student - GILDA BM08 c/o ESRF (Grenoble, FR)

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