[Ifeffit] Other programs than FEFF - GNXAS and MXAN

Matt Newville newville at cars.uchicago.edu
Thu Jul 27 14:10:26 CDT 2006

Hi Matthew,

I may be biased, but based on what I saw at the recent XAFS13
conference, I would not conclude that the 'international community
prefers GNXAS to FEFF' for EXAFS calculations.  I think a search of
the science citation index would show FEFF to be used somewhat
more (say, 10x) than GNXAS.  That's not to say that FEFF is better,
just that it is in wider use.

GNXAS does include both first principles calculations and analysis.
It has a very interesting approach for highly disordered systems
such as glasses,  where a single-shell cumulant expansion is known
to be bad.    It seems that these sorts of systems (solutions, glasses,
etc) are the primary use for GNXAS, though I don't know why that is.

In principle, it would be possible to use GNXAS calculations in Ifeffit.
Similarly, it would also be possible to use the outputs from EXCURVE
(which also does both 'first principle calcs' as well as analysis).   I
have not pursued either of these, but it's not out of the question.

MXAN (which I believe is by M. Benfatto, S. Della  Longa, and  C. R.
Natoli) is a 'full spectrum' XANES analysis program and seems like
a nice tool for fitting XANES,  including both the white line and first
EXAFS oscillations.  I've seen it applied (in very  nice papers from
Benfatto,  P.  D'Angelo, and others) to ions in solutions and medium-
sized biomolecules. I have not seen it applied to EXAFS, and think it
may not be appropriate for EXAFS, though I do not know for sure.


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