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

Stanislav Stoupin stousta at iit.edu
Thu Apr 15 12:16:01 CDT 2004

Hi Matt,

>> > 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.

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

Sorry for the confusion that I have introduced.
I am doing two-data set simultaneous fit (Bruce already mentioned that in the
list) where the two absorbers are Ru and Pt atoms
The model structure looks like this:
1. Ru data
2. Pt data

I was talking about the first part of the model
that is related to Ru data. What I meant was that around 1.0-1.5A I saw a
peak. According to the model that peak was a result of overlap of background and
contributions from different scatterers, such that I could not say
that the peak was primarily because of oxygen or any other scatterer.

I think the above was what you described as:
>'first shell peak', which is sometimes difficult
>to define for the asymmetric peak common with short metal-oxygen

Now if I set rmin=1.5A, the peak is not included in the R-range(it is
below rmin). At lower values of rmin a part of the peak is in the range.
That could be the reason why I was unable to get decent results with lower


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