[Ifeffit] Other programs than FEFF - GNXAS and MXAN

Matthew Marcus mamarcus at lbl.gov
Thu Jul 27 14:22:43 CDT 2006

One reason I can think of for GNXAS to be less popular than FEFF is that it 
hasn't been compiled
for Windows.  It exists only for various forms of Unix.  The website says 
that it's fortran, so there's no
reason I can see that it couldn't be compiled for Windows, depending on 
whether it needs some graphic
libraries.  Other reasons for the popularity of FEFF include its longer 
history, its distribution as source, so
it can be recompiled for any system, and not least, IFEFFIT/Artemis!

What is this 'interesting approach'?

MXAN seems to have a fit module which allows you to start with a cluster of 
atoms and automagically move
them around to improve the XANES fit.  By using XANES instead of EXAFS, you 
can apparently see quite
far out from the absorber.  A quick Google search didn't reveal any obvious 
way to acquire this package,
so it may not be publically available.  Anyone know where/how to get it?  It 
might make a nice compliment
to FEFF.

That reminds me - I'm a co-author on a paper, which was submitted to PRL, in 
which we used FEFF8.1
to simulate EXAFS.  A referee complained that FEFF8.1 was for XANES, not 
EXAFS.  What was that

----- Original Message ----- 
From: "Matt Newville" <newville at cars.uchicago.edu>
To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
Sent: Thursday, July 27, 2006 12:10 PM
Subject: Re: [Ifeffit] Other programs than FEFF - GNXAS and MXAN

> 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.
> --Matt
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