[Ifeffit] help: can I use ifeffit to predict chi?

Tai-Yen Chen tychen at mail.chem.tamu.edu
Fri Nov 2 12:53:38 CDT 2007

Hi, Bruce
   Thanks for the valuable information. I have tried the 
sum of pathes method to do the estimation.
But it seems like not to accurtate compared to the data I 
found in the paper.
So, I want to go back to the the proper fit fo find out 
poper sigma^2 and eo.
But I don't have any numeric chi data for gamma-Fe2O3. Do 
you have any idea where I may get these
information? Thanks for all the help.
Best Regard!!

On Thu, 1 Nov 2007 10:38:35 -0400
  Bruce Ravel <bravel at bnl.gov> wrote:
> On Tuesday 30 October 2007 21:21:59 Tai-Yen Chen wrote:
>> hi,
>>    Can anyone tell me whether I can use ifeffit to do 
>> job?
>> I want to know the % change in chi when the molecule 
>> 3% change in radius?
>> All I have is just the crystal struture of gamma-Fe2O3,
>> which means I can only get the Feff.
>> How can I introduce 3% change in redius so that I can 
>> the difference of chi?
>> Can anyone help me? Tanks a lot.
> Hi TaiYen,
> Since you are asking about using Ifeffit, I presume that 
>you are
> interested in changes in the EXAFS spectrum rather than 
>the XANES.
> There are a number of ways you might approach this 
>problem.  Probably
> the best way of doing so would be to do a proper fit to 
>measured data
> so that you can get a good measure of things like 
>sigma^2 and e0.
> Then, using the results of the fit, modify the deltaR 
>parameters for
> each path used in the fit to be 3% larger.  Then simply 
>add up the
> paths using the fitted values for sigma^2, e0, and so 
> You can also do something similar without actually doing 
>a fit to
> data.  Use Artemis or ifeffit itself to increase R for 
>each path and
> simply sum the paths without using fitted values for 
>sigma^2 and so
> on.  The easiest way of doing so would be to set deltaR 
>for each path
> equal to "0.03*reff".  That will expand the length of 
>each path by 3%,
> thanks to the magic of the special "reff" parameter in 
> Another way of doing this (and a decent way of doing so 
>for a XANES
> calculation) would be to use Feff's rmultiplier keyword:
>  http://leonardo.phys.washington.edu/feff/wiki/index.php?title=RMULTIPLIER
> HTH,
> B
> -- 
> Bruce Ravel  ----------------------------------- 
>bravel at bnl.gov
> National Institute of Standards and Technology
> Building 535A, Room M7
> c/o Brookhaven National Laboratory
> Upton NY, 11973, USA
> My homepage:    http://xafs.org/BruceRavel
> EXAFS software: 
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TaiYen Chen 979-739-7772
Department of Chemistry
Texas A&M University
P.O. Box 30012
College Station, TX 77842-3012

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