[Ifeffit] Evaluation of uncertainty using correlated Debye model + advices for the fitting of an hexagonal Co-foil

Bruce Ravel bravel at bnl.gov
Tue Apr 7 09:44:14 CDT 2015

On 04/07/2015 04:47 AM, Samy OuldChikh wrote:

> "However, these approaches are unsatisfactory for several
> reasons. First, there are typically many more independent DW factors
> in the XAFS MS path expansion than can be fit reliably to the
> available data. Second, the semiempirical models require separate
> fits to appropriate Debye or Einstein temperatures for each
> multiple-scattering path. And third, these models typically ignore
> anisotropic contributions, and hence do not capture the detailed
> structure of the phonon spectra and associated DW factors."

> I do not understand why for the case of multiple-scattering paths,
> separate fits of Debye Temperature are needed ?

That /is/ an odd part of that paper.  The last line of the bit you
quoted is a reason to do it that way.

> If each multiple scattering paths requires a different Debye
> temperature, I don't see the point to use the correlated Debye
> model.

That's right.

Of ocurse, the CDM presumes that the only thing that contributes to
the EXAFS sigma^2 is the acoustic phonon spectrum.  That's rarely a
good assumption.

> Or maybe it is still valid to group some multiple scattering paths
> like I did with one Debye temperature ?

Sure.  In practice, there is only so much information in the EXAFS


  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 535A
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/

More information about the Ifeffit mailing list