[Ifeffit] EXAFS simulations - peak too high

[Matt Newville]

Lisa,



On Mon, Feb 3, 2014 at 12:27 PM, Lisa Bovenkamp <lbovenkamp at lsu.edu> wrote:
> Hello.
>
> I am running some EXAFS simulations Au L3 on Au clusters with SR coating.
> In the outer shell Au sits between 2 S atoms. 4 Au atoms are in the neighborhood
> up to 3.5 Angström.
> Expecting two peaks in the chi(R) - one for Au-S and one for Au-Au (here
> it can be several little ones) I find that for 1 out of 5 sites the Au-Au
> peak is way too high.
> Is something in the FEFF code weighing an Au-Au path for this site
> too much? Does anyone have some ideas on that?
>
> Thanks,
> Lisa
>

I'm a little confused by what you're asking.  Is SR "scratch resistant"?

As Scott points out, you should not expect one peak for Au-S and one
peak for Au-Au in chi(R).  Au-Au will almost certainly give a double
peak in chi(R) due to the resonance in the scattering for heavy
scatterers.  When you say "for 1 out of 5 sites the Au-Au peak is way
too high", what are you comparing it too?  Are the path degeneracies
the same, is there any disorder term included in the simulation, etc.

But if you're running a simulation, wouldn't you know what scattering
paths contributed to the different peaks, and especially if the paths
include multiple scattering?

--Matt