Debye function model, Math expression
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
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/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Papers by F. Bridges, D. Haskel and T. Tyson seems to be just what you need.
Anatoly
________________________________
From: ifeffit-bounces@millenia.cars.aps.anl.gov [ifeffit-bounces@millenia.cars.aps.anl.gov] on behalf of NIRAWAT THAMMAJAK [n.thammajak@gmail.com]
Sent: Friday, May 11, 2012 12:26 PM
To: XAFS Analysis using Ifeffit
Subject: [Ifeffit] Debye function model, Math expression
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
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.govmailto: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/http://cars9.uchicago.edu/%7Eravel/software/exafs/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.govmailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.govmailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
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Anatoly I Frenkel -
NIRAWAT THAMMAJAK