I am trying to use the following CIF files to
generate the feff path at the As edge:
1- 'Iron(III) arsenate(V) dihydrate', Scorodite,
H4 As Fe O6'; space group P c a b; number 61; orthorhombic
and
2. Iron(III) tris(dihydrogenarsenate) pentahydrate
Kaatialaite, Fe (H2 As O4)3 (H2 O)5, P 1 21/n 1, number 14; monoclinic
and in both cases, after running Feff, I obtain
distances Fe-As that are not real.
For instance in scorodite I find a distance As-Fe = 1,71 A.
How can I overcome this problem?
Thanks,
Elsa
At 14:00 30/09/2010, you wrote:
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1. Re: Ifeffit Digest, Vol 91, Issue 28 (Matt Newville)
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Message: 1
Date: Thu, 30 Sep 2010 11:28:28 -0500
From: Matt Newville <newvi...@cars.uchicago.edu>
To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Ifeffit Digest, Vol 91, Issue 28
Message-ID:
<aanlktinrmxoi2and=h=a+bir5frg0rruw_upyy53s...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi Elsa,
On Thu, Sep 30, 2010 at 10:33 AM, Elsa Sileo <e_si...@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
zero.
Hope that helps,
--Matt
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- Release Date: 09/30/10 06:34:00
Dra. Elsa E. Sileo
Solidos Inorganicos
INQUIMAE - Dto. Qca. Inorganica, Analitica y Qca. Fisica; FCEN, UBA
Int. Güiraldes 2160, Pabellón 2, Piso 3, Ciudad Universitaria - C1428EHA
CABA - Argentina
Tel: (54 11) 4576 3380 ext. 113
Fax: (54 11) 4576 3341
e-mail: si...@qi.fcen.uba.ar
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