[Ifeffit] Low amp results

Bruce Ravel bravel at anl.gov
Mon May 28 09:49:13 CDT 2007

On Monday 28 May 2007, Joji Kuniya wrote:
> I analyzed EXAFS spectra of trace of Fe in lithium tantalate crystals. At
> first, I created the feff.inp file of LiTaO3. Then I changed central Li
> atom to Fe atom and added Fe atom at the Ta site. So that, the fitted
> results is good except amp(amp results is 0.3). I think that the model
> structure is good, but I can not understand why amp is too low. How do you
> think about this results? And, I tried to fitting treatment using GDS
> parameters. But, I do not know that the general method how to use the GDS
> parameters. Please tell me the general way of GDS manipulation. My PC runs
> under Win XP, and My Artemis runs under feff8 conditions. Thank you.
> Joji Kuniya

Hi Joji,

You don't really provide enough information to give a good answer to
your questions.  I suspect that your problem has something to do with
the fact that the amplitude and the various sigma^2 values are highly
correlated.  Without more information about how you are actually
parameterizing your fits, though, it is hard to comment on that value
of amp.

I am confused that you put Fe on both the Li and Ta sites.  Is that
actually reasonable?  Could be -- but my hunch is that Fe would prefer
to sit on the Ta site.  Having the wrong element on a site can do bad
things to a fit.

If you haven't done so already, I would recommend that you work
through Scott Calvin's ZnO example, which you can find at:


It is a very nice introduction to Ifeffit and Artemis and to the
Ifeffit way of thinking about exafs analysis problems.


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

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advance 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/

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