[Ifeffit] R quality factor in k space

Matt Newville newville at cars.uchicago.edu
Fri Apr 17 10:01:47 CDT 2009

On Fri, Apr 17, 2009 at 8:08 AM, Cammelli Sebastiano
<Sebastiano.Cammelli at psi.ch> wrote:
> In the case of a linear combination fitting on the k space performed by
> ATHENA, the <∆chi> needs a correction. Is it correct to write:
> R_factor ≡ < ∆chi(k space))> = √[ ∑ (chi_C(ki) – chi_E(ki))2 / ∑(
> chi_E(ki))2] ?
> Where Chi_C(ki) = x1*chi1(k)+x2*chi2(k)  : chi1 and chi2 are the EXAFS
> functions of the two reference samples used for the linear combination
> procedure and x1, x2 (with 0<x1,x2<1 and x1+x2=1) are their weight; Chi_E(k)
> is the EXAFS experimental function of the investigated sample.

Yes, I that is correct.  For fits in k-space, the chi data is often
k-weighted, in which case all the 'chi' functions in these formulae
should be the k-weighted chi(k).


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