[Ifeffit] The degeneracy and the coordination number

Christopher Patridge patridge at buffalo.edu
Wed Dec 26 07:51:09 CST 2012

Zhaomo Tan,

I think you have to set the path degeneracy to 1 because the model you 
used for Cu in Artemis has already found that there are 12 degenerate 
paths which make up the first scattering distance.  By setting it to 
one, you then create a fitting parameter for the coordination number 
CN.  You also must constrain the amplitude factor SO2 to some value 
because these parameters, N and SO2, are correlated.

SO2(somewhere between 0.8-1.0) * N (=1) * CN(guess parameter)

- Chris

Christopher J. Patridge, PhD
NRC Post Doctoral Research Associate
Naval Research Laboratory
Washington, DC 20375
Cell: 315-529-0501

On 12/26/2012 6:23 AM, Zhaomo Tian wrote:
> Dear all,
> I am confused about the degeneracy and the coordination number used in 
> the Artemis program.
> I want to get the coordination number of 1st shell of my copper 
> sample, so I set a guess number N1=12(initial guess) as the 
> coordination number which will vary during the fitting iteration, but 
> when I am looking at the 1st path's parameters, there is another N 
> appear which may stand for the degeneracy.The 1st path of copper model 
> is single scattering, so the degeneracy N equals coordination number . 
> But when I set N=12, the guessed N1 will have a value which is closed 
> to 1, only when I set N=1, the guessed N1 will have a value which is 
> closed to 12. It seems that N and N1 are reciprocals. But I think N 
> actually equals N1 in the single scattering case.
> So I am really confused, If I want to get coordination number of a 
> shell in a fitting, how can I deal with floated coordination number 
> and its path degeneracy N?
> Thanks so much.
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