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Re: question about feff
Dear Weikun,
>I am doing some feff calculations in the Ni-Ag binary system. When I
>used feff to calculate the Ag FCC K edge XANES, I found there is a
>high E0 shift (about 30 eV) in my calcualted results. I do not
>know what I did wrong in my input file or what else important
>issues shall I be careful with?
When you say there is a 30 eV shift in E_0 you probably mean the *absolute
energy* of the Ag edge calculated by FEFF at 25541 eV is about 30 eV
too high, and not the position of the Fermi level which is the
usual definition of E_0.
The FEFF calculation of the absolute energy is not meant to be
highly accurate, and errors of several eV for K-shells of large
Z atoms are not unusal. Thus you did nothing wrong in the input file.
To match FEFF and experiment you *always* have to shift the
FEFF absolute threshold to match experiment.
However, the Fermi energy i.e., the value k=0 of the EXAFS chi(k) should
be accurate to a couple of eV. Here k=sqrt(E-E_0) with E in rydberg
units.
Sincerely,
John Rehr