[Ifeffit] Independence of scattering paths?

van der Veen Renske Renske.vanderveen at psi.ch
Fri Sep 26 21:38:58 CDT 2008


I have a question concerning the independence of scattering pathways. I
fitted the EXAFS signal of a molecule consisting of 30 atoms (the
related FEFF calculation is called calc 1). To see the effect of the
surrounding solvent molecules in the chi(k) data, I added an O-atom in
the coordinate list of the FEFF input file at an arbitrary distance from
the absorbing atom (in this case Pt) and I re-ran FEFF (calc 2). As a
check within calc 2, I generated the sum of the same scattering paths
that were used in the fitting model of calc 1 using the therein obtained
structural fit parameters. The new O-atom was not included in this sum.
I expected the sum within calc 2 to be identical to the fit of calc 1
based on the fact that the original atoms can not sense the presence of
the new O-atom (independence of scattering paths). BUT: the resulting
sum was significantly different from the fit!

Am I overlooking something here? Aren't the calculated backscatter
amplitudes and phases independent from each other?

I am using Artemis version 0.8.007, Windows XP, Ifeffit 1.2.9.

Thank you!

Best regards,

Renske M. van der Veen
PhD student EPFL / PSI
Paul Scherrer Institut 
Swiss Light Source WSLA/210
5232 Villigen PSI

Phone: +41 56 310 5362
Fax: +41 56 310 3151
E-mail: renske.vanderveen at psi.ch
Web: http://lsu.epfl.ch

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