Re: [Ifeffit] Other programs than FEFF - GNXAS and MXAN

Dear all, One of the problems for GNXAS is that it can not be used for actinides like U, Th, Pt etc. I, personally, contacted A. Philiponi (was in 2002) to get right to use GNXAS for natural actinides in natural samples for nuclear waste management (not for nuclear Energy) and he refused. Hope the developers changed their mind since 2002. M. Harfouche Le 27 juil. 06 à 21:22, Matthew Marcus a écrit :

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 about? mam

----- Original Message ----- From: "Matt Newville" To: "XAFS Analysis using Ifeffit" Sent: Thursday, July 27, 2006 12:10 PM Subject: Re: [Ifeffit] Other programs than FEFF - GNXAS and MXAN

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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 _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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