[Ifeffit] Basic questions

Kelly, Shelly Shelly.Kelly at uop.com
Mon Apr 6 13:05:45 CDT 2009

Hi Andy,

I have a book chapter that details how to set the k-range for a data
set. It also talks about Rbkg in detail.  If you want a copy just send
me an email.  


> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-
> bounces at millenia.cars.aps.anl.gov] On Behalf Of Andy Connelly
> Sent: Monday, April 06, 2009 12:16 PM
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] Basic questions
> Some really quick basic questions. I am working with EXAFS spectra of
> silicate glasses at various edges (including S and Fe K edges) and I
> am having a really difficult time pinning down the structures. Clearly
> with glasses I can't always be sure of the oxygen co-ordination and so
> I have to refine this value which is one among many problems. Just to
> check I have things right:
> 1. Are there any problems if I set the R-range min to the same value
> Rbkg?
> 2. If I want to refine the degeneracy of a path can I write the
> expression "amp*N_1" in the SO2 box? (where the N box is set to 1) and
> then refine "amp" and/or "N_1"? where N_1 equivalent to the degeneracy
> and amp is effectively SO2. Clearly they will be highly correlated,
> but does a formula like this cause IFEFFIT any problems?
> 3. If, for initial fits, I am only interested in the first shell
> should I set R-range max to a lower value to isolate that shell and
> then increase it as I look at shells at longer distances?
> 4. If I have a calculated Fe3+-O path from a 4 and 6 co-ordinate
> reference are these equivalent? Obviously, they will give a different
> bond length and the MS paths will change but if I am only fitting a
> first shell is there anything different. I think the answer involves
> the muffin tin potentials but I'm a little out of my depth there.
> Any advice about solving glass structures more than welcome. Whatever
> I try I can't get realistic results out.
> Thank you for your time,
> Andy Connelly
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