[Ifeffit] Interatomic distances from feff paths

shelly Kelly dr.sdkelly at gmail.com
Thu Sep 30 20:35:10 CDT 2010

Hi elsa,

You can open the cif file with a text editor and check the parameters in the atoms page against what you find in the cif file.

Sometimes a shift vector is needed. Check the messages in artemis for the possible values to try.

If none of these work. Try sending us the cif file.

Good luck

On Sep 30, 2010 5:01 PM, Elsa E. Sileo <sileo at qi.fcen.uba.ar> wrote: 

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


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?



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>Message: 1

>Date: Thu, 30 Sep 2010 11:28:28 -0500

>From: Matt Newville <newville at cars.uchicago.edu>

>To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>

>Subject: Re: [Ifeffit] Ifeffit Digest, Vol 91, Issue 28


>         <AANLkTinRMxoi2ANd=H=a+Bir5FRG0rruw_UPYy53sfCE at 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_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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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: sileo at qi.fcen.uba.ar


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