[Ifeffit] FEFF8

[Bruce Ravel]

Hi Ivana,

On Wednesday 26 April 2006 06:52, Ivana Radisavljevic wrote:
> I have read in one of the papers of the authors A.I. Lebedev and I.A.
> Sluchinskaya that Pb scattering form factors in FEFF6 were not precisely
> determined. As I am dealing with the similar systems, Pb1-xMnxTe(In, Ga) to
> be precise, could You please tell me if this is also true for the FEFF8
> version (if it is true et all)?

I am not familiar with the reference you mention.  Perhaps if you gave
the full reference and better explained the troubles you are having,
one of us here on the list might be better able to comment.  In my
experience, I have been able to do good analysis with Feff6 on Pb L3
edge data.  Does anyone else here have a different experience?

> Another thing that bothers me is that all of the real part Furier
> transformed EXAFS spectra taken at the tellurium K edge, appear to have the
> first peak divided. Since there is no direct indication of the sub-shells'
> existence and having in mind the similar tellurium feature noticed in Your
> paper "Combined EXAFS and first-principles theory study of Pb1-xGexTe", I
> am wondering what this feature should represent?

Heavy atoms have a dip in their scattering amplitude in the middle of
the k-range.  The result of this is a feature in the chi(k) data that
resembles a beat.  A beat-like feature in k Fourier transforms into a
split peak in R.

This is one of the many reasons that the Fourier transform of the
EXAFS chi(k) is **NOT** a radial distribution function and should
never be refered to as such.  It is certainly true that chi(R) is
related somehow to the partial pair distribution function and it is
also true that, by doing analysis of the EXAFS, we can extract
information that allows us to reconstruct (in some manner and with
some level of success) the partial pair distribution function.  But
chi(R) is **NOT** an RDF.  In this case, the split in the peak has
much to do with the backscattering amplitude of the lead atom.

B

-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
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 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/