[Ifeffit] Linear Combination Fitting in Athena

Bruce Ravel bravel at anl.gov
Thu Sep 6 15:32:40 CDT 2007

Hi Skya,

On Thursday 06 September 2007, Skya Fawcett wrote:
> A couple questions about linear combination fitting in Athena:
> 1. There is the option of floating an E0 for the standards, is there any
> way to restrict how much it floats, ie. constrain it to +/-0.4eV shifts
> during fitting?

The e0s can be floated -- that's what the "fit e0" column is all about
in the table on the LCF page:


Alternately, you can click the "All standards use the same e0" button,
which is the same thing as applying an e0 to the data but not to the

There currently is no way to apply the sort of constraint that you
want in Athena.  (The same is not true of Ifeffit.  If you were to use
Ifeffit directly, you could build a XANES fitting model that imposes
that constraint.  But Athena does not provide a way of doing so within
its GUI.)

My standard comment on this topic is that if you take care to align
all of your data and you have the right set of standards, e0 shifts
should not be necessary.

> 2. If I am fitting normalized u(E), and only care about the XANES region
> at this point, is perfecting background removal needed? (I have, of
> course, carefully checked the pre-edge and normalization range).

Nope.  The XANES LCF fitting uses the normalized spectra.  That is
independent of how the background is removed.  Sounds like you are
doing the right thing.


 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
 Argonne IL 60439, USA                                fax: (1) 630 252 9793

 My homepage:    http://cars9.uchicago.edu/~ravel 
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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