Hi Mike,

Thank you for your reply and information you have shared. Totally agree that multi-species fit is murky.

Yes, I am aware of Martin McBriarty’s papers and the LCF+AIMD method explained. In fact, I am collaborating with Martin with running a similar calculation. Martin helped me understand this analysis/calculations.

Thank you,

Vineetha

From: Ifeffit [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Mike Massey
Sent: Monday, June 17, 2019 12:26 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Multiple species with Artemis

Hi Vineetha,

I am aware of some people doing (or at least attempting) multi-species shell-by-shell fits, but it's a pretty daunting task, depending on your system.

Another approach that some people have had success with (check papers by Martin McBriarty and colleagues) is a combination of LCF and structural and spectral modeling. The situation I am familiar with in that case is the use of a spectrum from an adsorbed species and the simulation of EXAFS from AIMD structural models to tease out the contribution of each species to the overall mixed spectrum. Martin is a big advocate of this approach, and it does seem to make otherwise intractable problems more tractable.

Personally, although multi-species shell-by-shell fitting would be perfect for the types of systems I like to work on and the types of questions I like to answer, I feel like there's already enough uncertainty in interpreting the EXAFS spectra in those systems. A multi-species fit just makes the interpretation even murkier.

On the other hand, the coupled AIMD approach actually seems less uncertain, since you can explicitly account for factors such as thermal vs static disorder (rather than lumping the two together). It seems to improve the quality of conclusions one can draw from complicated spectra.

Sorry I can't be more helpful,

Mike

On Jun 17, 2019, at 8:20 AM, Mukundan, Vineetha <VMukundan@sunypoly.edu> wrote:

Hi All,

A couple of questions. I was searching the previous threads to check if someone here had posted/explained an example with mixing parameters to find the % content of different constituents present in a sample with Artemis. This is for shell-by-shell fitting. Can Artemis fit multiple chemical species/phases to the experimental spectra simultaneously?

OR fit the samples spectra measured at 2 different edges with one or two phase simultaneously?

Don’t know if I searched far enough.  Apology if it has been discussed. In that case, could anyone please direct me to those threads.

Thanks you,

Vineetha

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