[Ifeffit] Interest in more accurate theoretical standards

Samuel T. Chill samchill at utexas.edu
Tue Mar 25 15:30:56 CDT 2014


Dear List,

I have noticed that EXAFS fits to Au foils at 298 K underestimate the known
equilibrium bond length. According to the CRC Handbook the lattice constant
at 298 K is 4.0782 +/- 0.0002 Å. This is a bond length of 2.884 Å. However,
in published EXAFS work[1] as well as fits that I have performed the bond
length is about 2.867 Å. The error is small -- about half a percent too
short -- but I am interested in using EXAFS to study relatively small
changes in bond length and I am curious about the resolution that can be
achieved.

I want to understand the source of this error. I think the two biggest
sources of error would be correlation between variables in the fitting
model and errors in the theoretical standard (FEFF6 in this case). The
random experimental error for a foil should be negligible. I would like to
know if it is possible to create a better theoretical standard using a more
ab initio approach.

Is anyone aware of any other software for performing more accurate EXAFS
calculations? It is okay if it is a very expensive calculation as I have
plenty of computer time.

I have seen that some DFT packages can perform XANES calculations, but I
have seen no mention of EXAFS.

Thanks,
Sam Chill


1. http://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.195419
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