Warning "e0 is greater than 10"
Hello Feff community, I am practicing on using Artemis to fit a UO2 XAFS data I measured. The parameters I used can be found from the pic attached. The Artemis project file is also attached. I have been getting this "e0 greater than 10" warning on many of my fittings. Will picking a slightly different E0 change the result much? Any suggestions on how to improve this fitting? Thanks! Ke -- Ke Yuan PhD Candidate Department of Earth and Environmental Sciences 1100 North University Ave 3021 C.C Little University of Michigan, Ann Arbor MI 48109-1005
Hi Ke Yes, if you change the position of your E0 in Athena, it will result in a shift in your fit parameters. However, don't simply shift your E0 just to avoid the warning. Take a look to see if Athena mispositioned it first but if you are confident that it is correct, then you might take a look to see if E0 is large because you are not using a good model to fit the data. E0 is highly correlated with the path lengths so if you are way off in the latter, it can have an effect on E0. carlo On Tue, 14 Oct 2014, Ke Yuan wrote:
Hello Feff community,
I am practicing on using Artemis to fit a UO2 XAFS data I measured. The parameters I used can be found from the pic attached. The Artemis project file is also attached.
I have been getting this "e0 greater than 10" warning on many of my fittings. Will picking a slightly different E0 change the result much? Any suggestions on how to improve this fitting?
Thanks! Ke
-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org
On 10/14/2014 02:20 PM, Carlo Segre wrote:
Yes, if you change the position of your E0 in Athena, it will result in a shift in your fit parameters. However, don't simply shift your E0 just to avoid the warning. Take a look to see if Athena mispositioned it first but if you are confident that it is correct, then you might take a look to see if E0 is large because you are not using a good model to fit the data. E0 is highly correlated with the path lengths so if you are way off in the latter, it can have an effect on E0.
Also make sure that you computed the XAS for the correct edge. That is, make sure you ran Feff for the L3 edge rather than the K edge! B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/
Hi Ke, Regarding the 'correct' E0 position, did you place it past the white line? I find that if there is a huge white line (eg. Au2O3 Au-L3 edge), I need to place E0 in Athena at any point past the white line but before (or not too far out) the EXAFS. This way, the energy shift values I get are much better, < 5 eV. But if I place E0 at the rising edge of the white line, I get big energy shifts. Might be useful--> http://www.slac.stanford.edu/econf/C060709/papers/031_TUPO129.PDF Best wishes, Sin Yuen -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Carlo Segre Sent: 14 October 2014 19:20 To: Ke Yuan Cc: ifeffit@millenia.cars.aps.anl.gov Subject: Re: [Ifeffit] Warning "e0 is greater than 10" Hi Ke Yes, if you change the position of your E0 in Athena, it will result in a shift in your fit parameters. However, don't simply shift your E0 just to avoid the warning. Take a look to see if Athena mispositioned it first but if you are confident that it is correct, then you might take a look to see if E0 is large because you are not using a good model to fit the data. E0 is highly correlated with the path lengths so if you are way off in the latter, it can have an effect on E0. carlo On Tue, 14 Oct 2014, Ke Yuan wrote:
Hello Feff community,
I am practicing on using Artemis to fit a UO2 XAFS data I measured. The parameters I used can be found from the pic attached. The Artemis project file is also attached.
I have been getting this "e0 greater than 10" warning on many of my fittings. Will picking a slightly different E0 change the result much? Any suggestions on how to improve this fitting?
Thanks! Ke
-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
On 10/14/2014 02:14 PM, Ke Yuan wrote:
Hello Feff community,
I am practicing on using Artemis to fit a UO2 XAFS data I measured. The parameters I used can be found from the pic attached. The Artemis project file is also attached.
I have been getting this "e0 greater than 10" warning on many of my fittings. Will picking a slightly different E0 change the result much? Any suggestions on how to improve this fitting?
Something seems funny about your data. Shelly explains fitting UO2 very clearly in doi:10.1021/es0208409. Your data does not look like her data. B
Thanks! Ke
-- Ke Yuan
PhD Candidate Department of Earth and Environmental Sciences 1100 North University Ave 3021 C.C Little University of Michigan, Ann Arbor MI 48109-1005
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-- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/
participants (4)
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Bruce Ravel -
Carlo Segre -
Ke Yuan -
Sin Yuen Chang