[Ifeffit] Question about using a proper model

Matt Newville newville at cars.uchicago.edu
Mon Oct 27 09:12:54 CDT 2014

On Mon, Oct 27, 2014 at 1:14 AM, pushkar shejwalkar
<pshejwalkar2004 at gmail.com> wrote:
> Dear All,
>             I am new to XAFS data analysis and have very limited knowledge
> about using modelling structures for XAS analysis. I am not sure as to if
> this question is directly related to Demter or XAFS analysis as such but its
> a part of it for sure.
>      Question number one
>  I am trying to analyze the sample I recently collected at SPring-8
> facility. The structure I am hoping to be formed during the reaction is more
> of a organometallic complex at silica interface. In order to establish the
> structure I was told that there are two methods I could use.
> 1) Use a counter part compound which is exact/looks like the structure I am
> hoping (so basically known compound) and then do traditional comparison
> method to establish the structure.
>       UNFORTUNATELY I cannot synthesize such compound in lab nor such
> material is available in literature ( including crystal structure).
> 2) is to use the model.
> right now for modelling such structure I am using Spartan program (again I
> have not used it earlier in my graduate work) So I want to know as to how to
> generate the models in order to get the correct crystal parameters? (atoms
> positions?) Is spartan good enough to do job? is there any other method for
> doing such fitting?

Sorry, I'm not familiar with Spartan -- it can probably generate a
list of atomic X, Y, Z, atomic_number coordinates.... is that correct?
 If so, converting that into a feff.inp input file is not too hard,
but if you haven't done that before, I'd suggest starting by running
Atoms on a crystal structure with roughly comparable composition and
the same central atom, and then it can be modified from there.

>     Question number two
> In order to get lower E0 values after the fitting, I read that there is a
> method to use in which delE value can be set to 0 intentionally and then
> recalibrating the spectra in athena again in order to accurately calibrate
> the E0. I read paper by Shelly kelly and Bruce Ravel. Also I have seen the
> steps in one of shelly kellys PDF formatted lecture, although I am still not
> sure about the exacts steps to take in order to do such calibration. Could
> someone explain me the steps in details (especially taking artemis files to
> athena and then using it as STD spectra for calibration purposes, I am
> confused about that)

Why is it important to you to get a lower value for E0?


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