Well, looks like i'm raising a nice discussion :)
Summarizing, if I understood well at the present moment the effect of polarization is not included in Artemis analysis. However, going back to my scientific problem i think that the main contribution will come from the 4 in-plane S atoms, so as a first approximation I can use the @S1.1@ path and try to fit my EXAFS with that neglecting the out-of-plane contributions.

By the way, i've tried the VPaths and I've found it a nice and powerful tool! Previously i used to do it by exporting the single paths, summing them up and then import it again as a new X(k)... I don't really read all the documentation and this is my fault!

Thank you for your help and for clarifying the issue about polarization that was not really clear to me, I'm looking forward for the next Artemis version :)

Eugenio

2015-05-24 23:37 GMT+02:00 Bruce Ravel <bravel@bnl.gov>:

On 05/24/2015 05:03 PM, Matt Newville wrote:

You mean Artemis wasn't creating a POLARIZATION card? But one can just
go in and add that the the Feff.inp anyway, no? The feff.inp file is
editable before running Feff with Artemis all the time, right? That
should be independent of pathfinder. Or do you mean something else?

I mean something else. The pathfinder did not consider polarization AND when Artemis ran the genfmt part of feff, the polarization card was not passed along. So, regardless of whether you edit the feff.inp window to included a POLARIZATION card, that information was not being passed to feff when the feffNNNN.dat file was generated. There's no convenient way to intervene in that step.

It's been years, with not much complaint, so I kind of forgot about it. My apologies to George Strbinsky -- I should have fixed it when he asked me about this a couple years ago.

All of that will be fixed soon, with the caveat that ellipticity will not yet be supported by Artemis. (So the "polarization in the plane" trick won't work in Artemis. Again, this is an Artemis shortcoming, not a Feff shortcoming.)

I understand VPaths, I think. But I meant simply "sum these paths
applying the current parameters, without fitting". That used to be
very, very simple and I always find it useful and instructive for
exploring the contributions from different paths. Now it seems I have
to set all values to "set", then change them to "guess" to really do a
fit. Am I missing something?

Well, I suppose it is possible that things aren't working as intended, but the intent is that you could make a VPath out of /all/ the paths (i.e. select "Mark all" from the Mark menu, then select "Make VPath" from the actions menu, then plot in k, R, or q). The intent also is that the current values for all parameters will be used when the plot is made. If no fit has been performed, the initial values will be used. It should not be necessary to change all guesses to sets just to make that plot.

I suppose that could be streamlined...

B

--
Bruce Ravel ------------------------------------ bravel@bnl.gov

National Institute of Standards and Technology
Synchrotron Science Group at NSLS-II
Building 535A
Upton NY, 11973

Homepage: http://bruceravel.github.io/home/
Software: https://github.com/bruceravel
Demeter: http://bruceravel.github.io/demeter/
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