[Ifeffit] How do I create a histogram based on R-space values

[Matt Newville]

Deepak,

On Wed, Dec 9, 2020 at 9:27 PM Deepak Varanasi <tirrano1 at gmail.com> wrote:

> Good evening
>
> May I also know how to calculate the necessary ingredients in building a
> histogram such as R and N?
>

The analysis of EXAFS to extract structural parameters is slightly
complex.  There is quite a bit of literature on how to do this. I may
suggest looking at the books listed at
https://xafs.xrayabsorption.org/tutorials.html, especially the two by Grant
Bunker and Scott Calvin.

I suppose R is just the R-space stuff so how do I calculate N?
>

Hm, well actually it kind of isn't.

> Is it simply the number of peaks in my R-space graph or something else
> entirely?
>

No, it is not simply the number of peaks in the plot of |chi(R)|.  The
positions and intensities of those peaks do depend on the distribution of
distances, g(R), but also depend in non-trivial ways on scattering factors
of the photo-electron created in the absorption process.

> I need to be able to construct the histogram to finish my thesis and
> graduate but I am still stuck on it. Hence, may I request your guidance on
> this please?
>

EXAFS data is not simply "converted" to a histogram of distances, g(R).
EXAFS does depend on g(R) and an analysis of the EXAFS signals can provide
information about the local structure.

I hope that helps, but it appears you are confusing |chi(R)| (the magnitude
of the Fourier transform of the EXAFS oscillations) with g(R).   They are
related, but that relationship is not simple enough to allow a simple
conversion from |chi(R)| to g(R).

--Matt
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