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 -- Bruce Ravel ------------------------------------ bravel@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/