Hello everyone, there seems to be an interesting exchange of ideas going on. Let me contribute a few ideas or bits of information: 1) I don't believe anybody holds the right to speak in the name of the "international community", whatever that means. The scientific process is rather complex and does not even necessarily adapt itself to rules of democratic representation (who votes?...). Obviously the peer review process is not ideal (see the referee with strange ideas about a particular version of feff) but it might be the best we have. 2) Merci, Francois, for reminding us about the recent history of XAS. At the recent XAFS 13 conference there was hardly any mention of AXAFS and multielectron excitations. Is there anyone willing to write a history of XAS to follow on the one by Ch. Brodeur? Might be an interesting endeavor. 3) I have been using both GNXAS and FEFF related software for many (say 15 - 20) years. Most of the differences have come up in replies in the past few days. One extra difference between GNXAS and FEFF I would like to point out is that FEFF treats (linear and circular) polarization dependence while as far as I know GNXAS does not (it didn't for sure until a few years ago). 4) The formalism underlying GNXAS is very elegant and reading the original papers is great. I suggest it is highly worth the effort. 5) Regarding ease of use: is XAS amenable to a "black box" approach? Despite the fact that this clashes with what many of us teach to physics students, it might be very useful e.g. in the field of bioXAS. But can this be done? Or is the underlying physics too complex? Cheers, Federico ----------------------------------------------------------------------------------------------- Prof. Federico Boscherini Department of Physics University of Bologna viale C. Berti Pichat 6/2 40127 Bologna (Italy) e-mail: federico.boscherini@unibo.it tel: ++39 051 209 5805 fax: ++ 39 051 209 5153 research web site: http://www.bo.infm.it/grp/fb/e2_home.htm sito della didattica: http://ishtar.df.unibo.it (seleziona Uni Bo, Scienze, Boscherini) ________________________________ From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Bruce Ravel Sent: Fri 28/07/2006 16:03 To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Other programs than FEFF - GNXAS and MXAN 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 better".
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? B -- Bruce Ravel ---------------------------------------------- bravel@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/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit