[Ifeffit] [EXTERNAL] Ifeffit Digest, Vol 206, Issue 8

[Matt Newville]

Hi Dien,

On Mon, Apr 13, 2020 at 2:02 PM Dien.Li at srnl.doe.gov <Dien.Li at srnl.doe.gov>
wrote:

> Hi, all
>
> I fitted my Cr EXAFS data, but E0 was -2.5. I calibrated the spectrum in
> energy space by +10 eV, the spectra in K and R space were identical before
> and after this calibration, in contract to my understanding that the k
> space oscillations and R magnitude should shift. Could you please provide
> any direction on how to get E0 to position values or negative E0 is
> acceptable? Thank you so much.
>
>
An E0 of -2.5 eV should not be a problem.  Basically, E0 gets selected for
an experimental spectrum in a pretty ad-hoc way (maximum of the 1st
derivative).   The Feff calculations also make an assumption about where
the energy threshold should be.  It's not unusual or a problem for these to
differ by a few eV.   We would start to get concerned if the difference
needed to be as large as 10 eV.  Now, sometimes that is reasonable, but it
can also indicate that the ligand or bond length is way off.

I don't know what you mean by "calibrated the spectrum in energy space
by +10 eV" -- you mean you added the number 10 to all energy points?  That
won't make a difference.

Hope that helps,

--Matt
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