[Ifeffit] E0 problem

Bruce Ravel bravel at bnl.gov
Mon Dec 19 14:04:19 CST 2016

On 12/19/2016 02:39 PM, Fuxiang Zhang wrote:
> Hi, All
> I have a problem about E0. It seems that E0 has great effect on the R(x)
> and the fitting. Can anyone explain how Athena automatically find the E0
> value from an EXAFS spectrum.
> Sometimes the value is not at the peak of derivative of u(E), shall it
> be corrected manually?
> Thanks

E0 is highly correlated with R because both E0 and R primarily effect 
the phase of the EXAFS equation.

The way I explain the meaning of the delta E0 parameter when I teach an 
EXAFS course is that it is the parameter that is used to align the 
wavenumber grid of the theory and the data.  That is, you choose an E0 
parameter in Athena to set the k grid of the data.  Feff does whatever 
Feff does to choose it's zero of k.  While the theory is quite good, 
it's not perfect, particularly near the Fermi energy.  There is nothing 
that guarantees that Feff's notion of the zero of k is consistent with 
your choice in Athena.

Hence, you need a delta E0 parameter in your fit.  And that parameter is 
highly correlated (in the numerical sense) with R.


  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 743, Room 114
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/

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