[Ifeffit] Analyzing EXAFS data on Artemis

Alexandros Deltsidis adeltsidis at iesl.forth.gr
Fri May 28 12:05:14 CDT 2021

Thank you everybody,

I definitely got some useful insights into my problem, which will help me
see this analysis towards a successful end.

Many thanks,

> Hi Alex,
> I agree with everything Carlo and Matthew said.
> As you say, Li is very light and so the scattering should be weak compared
> to Fe.  It will also die out much more quickly with "k" than the Fe (or
> Se)
> scattering will.  So, if you have enough k-range, simply starting your fit
> at higher k than normal (perhaps 4 or 5 Ang^-1) or increasing the k-weight
> used in the Fourier transform (perhaps to 3 or 4) would de-emphasize the
> Se-Li scattering to a level that it was safe(r) to ignore.
> FWIW, I would imagine that trying to fit coordination number or sigma^2
> for
> Se-Li at percent-level concentrations would not work very well. If you did
> indeed get values that were clearly telling you that there was definitely
> Se-Li scattering contributing, I would wonder if there was something else
> going on (say, from another ligand, some multiple scattering, or some
> other
> phase).
> The formula for the Einstein temperature is a scale factor times
> "coth(theta/(2t)) / (r_mass * theta)"  where t is the temperature, theta
> the Einstein temperature, and r_mass the reduced mass of the atoms in the
> path.   See
> https://github.com/xraypy/xraylarch/blob/726136d0184d9a006546002722b7573f6c675357/larch/xafs/sigma2_models.py#L19
> for details.  This will not include S0^2 -- they are conceptually totally
> different.
> As Carlo said, the sigma^2 in the EXAFS equation does not distinguish
> between static and thermal disorder.  But if you have
> temperature-dependent
> data, modeling the sigma2 values as a static offset + a term that depended
> on temperature with an Einstein model would be a fine way to go.
> Hope that helps!
> On Thu, May 27, 2021 at 9:43 AM Alexandros Deltsidis <
> adeltsidis at iesl.forth.gr> wrote:
>> Dear mailing list,
>> I am currently analyzing some EXAFS data. I am studying a Lix(C5H5N)FeSe
>> system in a temperature grid that extends from 20 K to 300 K and I have
>> 4
>> such datasets which correspond to different amount of doping (x). Right
>> now, im focusing on fitting the 1st coordination cell, in Artemis for
>> the
>> Se K-edge. My starting model is the simple P4/nmm FeSe. So, in my system
>> the 1st coordination cell, in the Se K-edge, co

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