[Ifeffit] Help

Bruce Ravel bravel at bnl.gov
Fri Oct 3 13:12:40 CDT 2014


I see that you haven't yet received an answer to your question.  I 
suspect that's because you've asked a very broad and open ended 
question.  I'll try to get you pointed in the right direction, but you 
are going to have to spend some time studying up on how to perform EXAFS 

The error you are citing is from Artemis complaining that you are trying 
to over use the amount of information in the data set.  The information 
content of an EXAFS measurement is approximated from it's bandwidth, 
that is the extent of k-range of the Fourier transform multiplied by the 
extent of fitting range.  Specifically,

   Nidp <= 2 * (kmax-kmin) * (Rmax - Rmin) / pi

That is, the bandwidth represents an upper bound on the information 
content of the data.

It would seem that you have either a very short k-range or a very short 
R-range such that Nidp is only 2.

I think you are not doing yourself a favor by starting your EXAFS 
analysis career with a material as disordered as zirconia.  It's a low 
symmetry space group, none of the atoms are at symmetry centers.  It's 
just a hard analysis problem.  I think you need to practice on something 
much simpler, a metal or a high symmetry oxide.

You should also consult some of the training material that is available 
on the web.  There is a ton of good information at 
http://xafs.org/Tutorials.  If you go to the Demeter home page and 
scroll down to the documentation section, you'll find links to videos of 
lectures I gave at Diamond about using the software.  Following along 
with those, then repeating all the analysis on your own seems like a 
good idea.  Getting a copy of either of Scott Calvin's or Grant Bunker's 
recent books on EXAFS would be a good idea, as well.


On 09/30/2014 02:43 PM, johnny huertas wrote:
> Good afternoon:
> My name is Jhonny, I work at PUC-Rio in Brazil and I'm having hard
> difficult to fit the ZrO2 tetragonal. I create the INP file using the
> follow structural data
> Space group: p21/c
> a=5.1490
> b=5.2070
> c=5.3160
> alpha=90
> beta=99.2250
> gamma=90
> Zr (0.2750; 0.03900; 0.2090)
> O (0.0650; 0.3260; 0.3100)
> O (0.4610; 0.7570; 0.4790)
> Several paths were created, but when I start to fit each path a message
> of ABORT appear saying "you have 3 variables but only 2 independent
> measurements in 1 data set"
> One more thing, each path has 1 coordination number (deg)
> I don't know what to do, I need some help.
> Thank.
> Jhonny Huertas Flores
> Rio de Janeiro-Brasil
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  Bruce Ravel  ------------------------------------ bravel at 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/

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