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

Frenkel, Anatoly frenkel at bnl.gov
Tue Mar 27 10:22:45 CDT 2007


Mauro, 
 
If I do understand your question correctly, you may be asking how to handle a multiple of inequivalent sites in atomic clusters with N atoms, where each atom generates a unique sequence of single- and multiple-scattering paths. A possible solution is given in this article:
 
D. Glasner and A. I. Frenkel 
Geometrical characteristics of regular polyhedra: Application to EXAFS studies of nanoclusters 
AIP Conf. Proc. 882 , 746-748 (2007). <https://exchange2000.bnl.gov/exchange/frenkel/Drafts/RE:%20%5BIfeffit%5D%20%5Bhowto%5D%20configurational%20average%20in%20EXAFS%20with%20FEFF.EML/XAFS13-Proc/clusters-geometry.pdf>  
 
The PDF is here:
 
http://pubweb.bnl.gov/users/frenkel/www/XAFS13-Proc/clusters-geometry.pdf
 
It is the same type of averaging and radial distribution analysis approach that you are proposing unless I misunderstood your question.
 
Anatoly
 

________________________________

From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of Mauro Rovezzi
Sent: Tue 3/27/2007 9:38 AM
To: Ifeffit-ML
Subject: [Ifeffit] [howto] configurational average in EXAFS with FEFF



Dear all,

I would like your point of view on how to approach configurational
average in EXAFS analysis with FEFF (let's not consider GNXAS for the
moment).

In particular, I'm trying to combine ab-initio DFT numerical simulations
with EXAFS for doped semiconductors where in the minimized cluster there
are N absorbing atoms.

Usually I don't use the CFAVERAGE card because fractional degeneracies
are not taken into account and, to have a qualitative analysis, I
calculate an "extended"-XANES (up to 8.0 A^-1) for each cluster - where
each absorbing atom is shifted to (0,0,0) - and then I average over all
single-cluster signals.

Well, at this point my question is: how to proceed in the quantitative
analysis with Ifeffit? In fact, considering only single-scattering
expansion for all the clusters the result could be seen as a radial
distribution for each scattering pair where the integral gives the
coordination number and the FWHM a structural Debye-Waller factor. How
to combine these informations?

Thanks for the answers,
Mauro

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