Re: [Ifeffit] Large Enot values

Thanks Shelly. I have tried doing as you suggest, shifting manually the value of E0 by +10 eV in Athena before fitting in Artemis. Thankfully the delta E of the new fit is close to zero which I think means that the theory and the data do agree, i.e. I am fitting the first shell with the correct atom type. I am still a little unclear as to why such a large energy shift might arise and will look into this further. Any tips or suggestions would again be very welcome and I would very much appreciate it if you can send me a copy of your book chapter which you mentioned. Best Regards Paul. -- Dr. Paul Bingham Postdoctoral Research Associate Immobilisation Science Laboratory Dept. of Engineering Materials University of Sheffield Mappin Street Sheffield S1 3JD UK Email: p.a.bingham@sheffield.ac.uk Direct Line: (0114) 2225473 Quoting ifeffit-request@millenia.cars.aps.anl.gov:

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Today's Topics:

1. Re: Large Enot values (shelly Kelly)

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Message: 1 Date: Fri, 11 Jun 2010 09:18:33 -0500 From: "shelly Kelly" To: "XAFS Analysis using Ifeffit" Subject: Re: [Ifeffit] Large Enot values Message-ID: <4c1245c4.9d90d80a.567d.3528@mx.google.com> Content-Type: text/plain; charset="utf-8"

Hi  paul:

Have you tried to shift eo in athena by 10 ev? If you have and the fit still gives a large deltaE then the theory and the data do not agree.  DeltaE changes the spectra most strongly at low k, so another thing to try is to increase kmin in the ft. 

You can also use the theory to help remove the background in athena.  If you have tried all these and it doesn't work.  I'd try a different theory.  Either a different se oxide or a different atom type.

Of course my book chapter goes over how to do these thing. I'll send you a copy if you ask.  I've also posted example athena projects on xafs.org.

Good luck.

-- Sent from my Palm Pr? On Jun 8, 2010 5:55 PM, Paul Bingham <p.a.bingham@sheffield.ac.uk> wrote:

Thanks Bruce,

I agree that the Se-O bond lengths are short but in SeO2, and Na2SeO3 as Se4+

"standards" there are Se-O bond lengths average around 1.7A. For example when I

run feff on the SeO2 cif file it gives 1 Se-O bond at 1.623A and 2 at 1.793A,

averaging at roughly 1.7A.

I'm confident that the XANES I have for this sample show that the Se is pretty

much all present as Se4+ and I think the first shell is very likely to consist

of oxygens.

I also tried another shell from the same feff as included in the data I sent,

using O1_1 instead of O2_1 and the fit including Delr still points to an

average Se-O bond length of about 1.7A with an Enot of around 10.

I will try fitting with feffs based on different cif files with some different

Se-O bond lengths, but if you have any other suggestions I'd be grateful.

Thanks very much for your advice - it's appreciated.

Regards

Paul.

--

Dr. Paul Bingham

Postdoctoral Research Associate

Immobilisation Science Laboratory

Dept. of Engineering Materials

University of Sheffield

Mappin Street

Sheffield

S1 3JD

UK

Email: p.a.bingham@sheffield.ac.uk

Direct Line: (0114) 2225473

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