[Ifeffit] Odd feff result

[Bruce Ravel]

On Friday 24 March 2006 13:01, Scott Calvin wrote:
> So here's the question. These three paths are identical except for
> the identity of one of the scattering atoms. The degeneracy of the
> path with boron and the path with nickel is the same. Why is the feff
> amplitude ratio for the boron-containing path higher than that of the
> nickel-containing path? Shouldn't nickel scatter more strongly? And
> yes, I double-checked...the potentials are defined correctly in the
> feff.inp file.

Scott,

I am inclined to side with Jeremy and Feng.  One might be surprised by how 
quick-n-dirty the amplitude calculation is.  If memory serves (and who knows 
how likely *that* is), feff computes the complex chi(k) using plane waves, 
which is a very quick calculation.  It then adds up the magnitude of the 
complex chi(k) at 4 points.  That's it.  The amplitude is never meant to be 
more than a guide to eye.  As you well know, to know how each path 
contributes to the data, you actually need to plot them or -- better -- do a 
fit.

B

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