[Ifeffit] Third cumulant in DWF

[Matt Newville]

Hi Matthew,

On Mon, Apr 4, 2011 at 5:51 PM, Matthew Marcus <mamarcus at lbl.gov> wrote:
> OK, so if you don't add a sigma2 to your FEFF input file, then IFEFFIT will
> do the correction properly.  Another question
> is whether, if you add a sigma2 to feff.inp, what does FEFF do?
>        mam

FEFF's ff2chi module does apply sigma2 to the complex photoelectron
wavenumber. It does not make the correction for the 1/R^2 term
described by Tranquada and Ingalls.

Like Bruce says, for general use, putting sigma2 and S02 in feff.inp
can be somewhat confusing, as these are not applied to the
feffNNNN.dat files that feffit/ifeffit/artemis uses, but only to the
chi.dat file.

In some sense, feffit/ifeffit/artemis were  written as replacements
for FEFF's ff2chi module, summing path contributions with sigma2, S02,
 and a few more bells and whistles.

--Matt