[Ifeffit] Other programs than FEFF - GNXAS and MXAN

Bruce Ravel bravel at anl.gov
Fri Jul 28 09:03:22 CDT 2006

On Thursday 27 July 2006 14:22, Matthew Marcus wrote:
> Other reasons for the popularity of FEFF include its longer history, 

Actually the early references for both GNXAS and FEFF6 date from 1991.

To paraphrase Steve Zabinsky (the fellow who did much of the work on Feff6) 
"if you make it easy to use, everyone will use it -- even if it's not 

> its distribution as source, so  
> it can be recompiled for any system, and not least, IFEFFIT/Artemis!

I'd say that today this mailing list contributes to Feff's wide adoption at 
least as much as the codes that are the topic of the list.

> What is this 'interesting approach'?

Matt and I were solving materials physics problems in grad school, so our 
codes are very well suited to problems involving crystals or other things 
with fairly well known atomic positions.  Adriano and Andrea were (I think, 
but I could be mistaken) solving problems more along the lines of solvation 
chemistry and highly disordered material.  Consequently (and explained in 
broad brushstrokes) GNXAS is well suited to problems for which the g(R) is 
not described by discrete atomic positions.  In essence, GNXAS integrate the 
exafs equation over a functional form of g(R).  It is certainly possible to 
deal with high disorder in Feff-base analysis and it is certainly possible to 
do material science-y problems with GNXAS -- they really aren't that 
fundamentally different.

If you are looking at amorphous solids or solvated ions (or really any other 
system) you would be wise to look into GNXAS.  You may find that it fits your 
problem or fits into your brain better than Feff, Ifeffit, and my software.

> 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?

Ummm.... a high degree of confusion on the part of the referee perhaps?


 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
 Argonne IL 60439, USA                                fax: (1) 630 252 9793

 My homepage:    http://cars9.uchicago.edu/~ravel 
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/

More information about the Ifeffit mailing list