[Ifeffit] R quality factor in k space

Cammelli Sebastiano Sebastiano.Cammelli at psi.ch
Fri Apr 17 08:08:11 CDT 2009

Dear iffefit user,

I found on a paper (E.A. Stern et al. /Physica B 208&209 (1995) 117 120) the definition of R quality factor as:


R_factor ≡ < ∆chi(R space))> = √[ ∑ |chi_C(Ri) – chi_E(Ri)|2 / ∑( chi_E(Ri))2]   ----> formula 3 


Where Chi(Ri) is a complex function (imaginary and real part of the XAFS spectra in the R space), C concerns the calculated XAFS spectrum, while E refers to the experimental XAFS spectrum. 

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.


Best regards


Sebastiano Cammelli 




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