[Ifeffit] Question about FEFF6

goodhei8 at gmail.com goodhei8 at gmail.com
Tue Apr 12 22:04:42 CDT 2011

Thanks a lot for the detailed answer.


Jack Song

On 2011-04-12 09:03, Bruce Ravel wrote:
> On Tuesday, April 12, 2011 03:24:22 am goodhei8 at gmail.com wrote:
>> 1, FEFF takes Z atoms at equal distance as same. It does not care some
>> have neighbor A, some have neighbor B. Should I worry about it? and when?
> In Feff6, two atoms that are at the same distance and have the same
> unique potential make the same contribution to the EXAFS.  I don't
> quite understand what you want to worry about.
>> 2, Does FEFF consider about valence state (like Ur 3 or Ur5 in center)?
> Feff6 does not understand valence.  This is one of the differences
> between Feff6 and Feff8.  Feff8 uses a self-consistency loop to
> transfer charge between the atom types, resulting in something that
> can be related to formal valence in some situations.
> The follow-up question you have to ask is whether EXAFS analysis is
> actually sensitive to charge transfer.  In the regime in which the
> EXAFS fit is evaluated, the photoelectron has large kinetic energy and
> is not particularly sensitive to the details of the potential surface.
> In almost all situations, Feff8 is a modest improvement at best over
> Feff6 for EXAFS analysis.  That is why we continue to distribute and
> use Feff6 with Ifeffit and Artemis.
> Of course, charge transfer is a dramatic effect in the XANES.  But you
> were asking a question about EXAFS analysis.
> B

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