On Tuesday, March 26, 2013 01:21:58 PM Matthew Marcus wrote:
Just to put my bit in, I believe that the most significant advantage of higher FEFF versions for EXAFS analysis is that it results in more reasonable values for E0 for high-Z elements. I forget whether the issue is high-Z scatterer or absorber. If you use any of the common prescriptions for defining E0 with, say, Pt metal in FEFF6l, your fit will want large values of enot. That said, I have not done a real test by comparing FEFF8 and FEFF6 paths. Has anyone done that?
This is *exactly* my point. Except, as Matt said, for the rather limited, unpublished tests made by him and John many years ago, no one has reported on a substantive test comparing the efficacy of feff6 and feff8 for analysis of EXAFS. (Of course, computation of XANES and other spectroscopies is a different topic entirely.) Perhaps I would be more interested in fully implementing use of feff8 in my software if someone would offer a better justification than "8 is a bigger number than 6". FWIW, I agree with Matt that the multi-pole self-energies is a very promising thing that could have a substantial impact on EXAFS analysis. But few of those who claim to want to use feff8 with my software are actually computing and using the multi-pole self-energies. In any case, I do not have permission to redistribute feff8. So, on a very real level, this conversation is moot. B
It would be interesting to know what happens if you simulate a k^n*chi(k) with one program and fit it with the other.
-- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel