[Ifeffit] Re[2]: a question about background refinement

[Matt Newville]

Hi Stanislav, 

> >Normally, you'd want to keep
> >Rbkg/Rmin below the 'first shell peak', which is sometimes difficult
> >to define for the asymmetric peak common with short metal-oxygen
> >distances, but if the peak is around 1.3Ang, the Rbkg/Rmin of 1.5Ang
> >seems like it might be too high.  Can you get decent results with
> >a lower Rbkg/Rmin?
> No, I can not. 1.5A is around the minimum value in Chi(R) magnitude
> where the first peak can be separated from the others. However, the peak
> is a result of superposition of background, oxygen path and also
> the alloy structure.

I think I don't understand this.  What are the "others" that the
first peak can't be separated from??

> I have two e0 parameters in the model that correspond to ru and pt
> data sets (they are e0_ru and e0_pt)
> the same e0_ru I use for Ru-O path
> Typical values that they take are about:
> e0_pt           =     7.2318013   +/-      1.0171952    (0.0000)
> e0_ru           =    -9.1526876   +/-      0.7730603    (0.0000)
> 
> and this is consistent through all data that I have and also their
> values almost do not depend on whether I use rmin=1.0A or 1.5A

Two e0's that differ by 16eV for metal-metal bonds seems strange.  
I'd guess that Pt and Ru would be easily distinguished in the fit,
but also that E0 would not be dramatically different for these.  
Are you sure there's not something weird going on with these being
out-of-phase or something??  I could believe it's possible, but if
you look at the different fit components look in k- and r-space does
it all seem to add up as you would expect?
 
Sorry to be so slow in responding....

--Matt