[Ifeffit] Question about shift in E0

[Matt Newville]

HI Brandon,

If I understand right (and to echo Darius's questions), it seems like
you measure samples with a metal reference, and aligned the spectra in
Athena so that the references matched.  That's a fine way to go.   I
would ask: how big were the needed energy shifts?
Are the experimental mu(E) spectra aligned well at this point?   If
you're studying metal oxides with different oxygen content, you might
very well see oxidation in the XANES.   If I understand correctly,
you're saying you don't see this.

Then, you extracted the chi(k) from the aligned spectra.  How much did
E0 vary for the shifted spectra in this background-subtraction step?

Then, you pulled these chi(k) into Artemis, and see different E0
shifts in the fits.  This E0 is a little different, in that it is the
E0 shift applied to the Feff calculation to match the experimental
spectra.  If you use different paths or different calculations, such
E0 shifts might happen, and wouldn't be highly meaningful.

I know that's not a complete answer, but hopefully that and Darius's
questions will help,

--Matt

PS on  Q2: 1/ (kR)^2 vs 1 / kR^2

This is probably either a typo, or a different convention based on the
definition of f(k) as the electron scattering amplitude.   In the Feff
world, it should be 1/kR^2, but using 1/(kR)^2 would just map f(k) to
k*f(k).