[Ifeffit] Ifeffit Digest, Vol 91, Issue 28

Matt Newville newville at cars.uchicago.edu
Thu Sep 30 11:28:28 CDT 2010

Hi Elsa,

On Thu, Sep 30, 2010 at 10:33 AM, Elsa Sileo <e_sileo at yahoo.es> wrote:
> Dear Matt,
> I have to perform EXAFS analysis, and when I tried to fit the first
> shell, I found deltaE0 values of about 8 eV. Following the paper of
> Kelly et al (Analysis of soils and minerals using X-ray absorption
> spectroscopy. In Methods of soil analysis, Part 5: Mineralogical
> methods; 2008; pp 446) I fitted the first shell obtaining values for
> deltaE0, sigma^2; delta R and amplitude. Then, using the obtained
> values, and making deltaE0=0, I got the theoretical signal.

Why is important to have a theoretical spectra with deltaE0=0?

> When I compare the experimental and theoretical spectrum I see a mismatch
> between the position of the nodes at low wavenumbers.

Yes, that is what E0 does.

> Having done this, how I have to proceed to correct the experimental
> data in order to obtain smalller delta E0 values?

I think what you are trying to do (though I don't understand why) is
to adjust E0 for the experimental data so that the fit to a particular
theoretical standard gives deltaE0 close to zero.  If so, you want to
adjust E0 in the background subtraction.  If you change E0 by 8eV
there, you should end up with a deltaE0 in the fit that is close to

Hope that helps,


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