Hello,

May I add more questions to this. I do a research on magnetic materials. Bond lenghts and geometries are really important to understand the magnetic interactions and I think EXAFS is the promising tool for this. I have measured the EXAFS spectra for quite a complex material system. There are 3 sites of absorbing atom (Fe) in the crystal structure, therefore I created 3 FEFF models to fit the data with different amplitudes. Closest neighbours are oxygen atoms, and then Li. The strongest scatterers are La atoms sitting ~4.26 angtrom away from the absorbing atom, which contribute a significant 3rd shell. Yes, there are many paths to include. Math expressions together with bulk structure details obtained from neutron diffraction help to minimise the parameters somewhat. However, there are thermal factorss, very small but too many of them.

I measured my sample at 1.5 K, then sigma^2 are quite small. Could you please suggest any papers, models, or math expressions constraining these factors at low temperature. Would it be sensible to constrain them as 0, or a range of small numbers obtained from the significant shells?

Thank you very much,
Nirawat.

On 24 August 2010 18:25, Frenkel, Anatoly <frenkel@bnl.gov> wrote:
Just to add:
These procedures, described in that article, can be easily implemented in Mathematica.
Anatoly
 

From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Ravel, Bruce
Sent: Tue 8/24/2010 1:23 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] debye function

On Tuesday 24 August 2010 12:23:18 pm Kleber Daum Machado wrote:
>   Hi,
>
> I'd like to know the explicit mathematical expressions that are
> represented by the functions debye(temp,thetad) and eins(temp,thetae).
> Are they given in some documentation file or article?

See

"Extended x-ray absorption fine structure Debye-Waller
factors. I. Monatomic crystals"
E. Sevillano, H. Meuth, J. J. Rehr
Phys. Rev. B 20, 4908–4911 (1979)
http://link.aps.org/doi/10.1103/PhysRevB.20.4908

B


--

 Bruce Ravel  ------------------------------------ bravel@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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