[Ifeffit] Warning "e0 is greater than 10"

[Sin Yuen Chang]

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 at millenia.cars.aps.anl.gov [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Carlo Segre
Sent: 14 October 2014 19:20
To: Ke Yuan
Cc: ifeffit at 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 at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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