[Ifeffit] Artimis

[Matt Newville]

Scott, Michel,

Scott Calvin wrote:
> 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.

Michel Jauoen wrote:
> 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).

Interesting -- I haven't seen this effect, but I probably haven't
looked very hard either.  I don't think that having an E0 'closer
to the experiment' is a significant gain, as it still is relative
to the experimental E0 (which is usually the fairly ad-hoc
max-of-derivative) and has to be refined in the fit.  

But if it can reduce the number of situations where you need 2
E0's, that could be important.  I think it's still not well
understood when multiple E0's are needed, but having some insight
on where Feff8's SCF is noticeably better might be a good start.  
Would one of you be willing to send an example, and/or maybe give
some indication of what sort of systems would need 2 E0's with
Feff6 and 1 E0 with Feff8?


Thanks,

--Matt