[Ifeffit] schemes for delr and sigma2 for multiple scattering paths

[Scott Calvin]

Jatin,

IF the uniform expansion model is valid for single scattering paths,  
then it is for multiple scattering paths as well. For some materials,  
particularly those with cubic space groups, that's got a good chance  
of being a useful model. Others tends to distort with changes in  
temperature, doping, etc., and it may not work as well. But even in  
those cases, if you've decided how to constrain the delr for single- 
scattering paths, you'll do reasonably well by using some kind of  
appropriate average of the delr's for related single-scattering paths.

--Scott Calvin
Sarah Lawrence College

On Oct 7, 2010, at 3:05 AM, Jatinkumar Rana wrote:

> Dear all,
>
> It is reasonable to assign a constant fraction by which unit cell
> expands at a given temperature of XAFS measuremnt and so the variation
> in the path lengths for every single scattering paths could be  
> assigned
> as delr = alpha * Reff. Similarly, one can assign  sigma2 value for  
> each
> single scattering path depending on both type of scatterer and its
> distance from the absorbing atom.
>
> Now coming to multiple scattering paths, Sigma2 for multiple  
> scattering
> paths can be constrained based on the sigma2 of related single
> scattering paths and a definite path-geometry-dependent scheme
> (Triangle, collinear, reversed etc.) could be applied.
>
> Is there any such scheme for delr of multiple scattering paths ? or we
> can simply assume that all paths (single scattering and multiple
> scattering) undergo uniform expansion by a factor alpha.
>
> Thank you so much in advance for your valuable time...
>
> With best regards,
> Jatin Rana
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