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

[Bruce Ravel]

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
spectrum.

B


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