Interatomic distances from feff paths
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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Today's Topics:
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
To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Ifeffit Digest, Vol 91, Issue 28 Message-ID: Content-Type: text/plain; charset=ISO-8859-1 Hi Elsa,
On Thu, Sep 30, 2010 at 10:33 AM, Elsa Sileo
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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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@qi.fcen.uba.ar
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 Shelly On Sep 30, 2010 5:01 PM, Elsa E. Sileo <sileo@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 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: >Send Ifeffit mailing list submissions to > ifeffit@millenia.cars.aps.anl.gov > >To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >or, via email, send a message with subject or body 'help' to > ifeffit-request@millenia.cars.aps.anl.gov > >You can reach the person managing the list at > ifeffit-owner@millenia.cars.aps.anl.gov > >When replying, please edit your Subject line so it is more specific >than "Re: Contents of Ifeffit digest..." > > >Today's Topics: > > 1. Re: Ifeffit Digest, Vol 91, Issue 28 (Matt Newville) > > >---------------------------------------------------------------------- > >Message: 1 >Date: Thu, 30 Sep 2010 11:28:28 -0500 >From: Matt Newville <newville@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_UPYy53sfCE@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@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 > > >------------------------------ > >_______________________________________________ >Ifeffit mailing list >Ifeffit@millenia.cars.aps.anl.gov >http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > > >End of Ifeffit Digest, Vol 91, Issue 30 >*************************************** > > >No virus found in this incoming message. >Checked by AVG - www.avg.com >Version: 8.5.445 / Virus Database: 271.1.1/3168 >- 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: sileo@qi.fcen.uba.ar _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffi
participants (2)
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Elsa E. Sileo
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shelly Kelly