[Ifeffit] Re: Ifeffit Digest, Vol 20, Issue 22

[Bruce Ravel]

>>>But also: why would you use Feff8 for EXAFS analysis, as with
>>>artemis??  Feff8 is a XANES code. As far as I know, it does not
>>>give any improvements for EXAFS.
>>
>>
>>FEFF8 does give at least one improvement for EXAFS, which I've used
>>on occasion: the self-consistent field calculation can be used to
>>give an improved estimate of E0 prior to fitting.
>>
>>--Scott Calvin
>>Sarah Lawrence College
>>
>
> I agree with Scott: SCF calculation gives more reliable estimate of
> E0 because the Fermi level is more accurate. It makes that, when
> several atomic species are involved, you only need in principle one
> E0 for fitting (I have verified this point, at least for the case I'm
> presently working on).

This is an interesting question.  Way back when, when Feff8 was being
developed, there was some discussion about how big an effect
self-consistency would have on the e0 parameters used in exafs analysis. 
To my knowledge, no one has really done a systematic survey of this effect
in a variety of systems (i.e. well-ordered, highly disordered, metallic,
covalent, ionic, and so on).  It seems like a good thing for some one to
work on and publish, so that we have a better basis for conversations like
this one.

B