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

I have sent Chen some data on magnetite and maghemite. mam ----- Original Message ----- From: "Tai-Yen Chen" To: ; "XAFS Analysis using Ifeffit" Sent: Friday, November 02, 2007 10:53 AM Subject: Re: [Ifeffit] help: can I use ifeffit to predict chi?

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 wrote:

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On Tuesday 30 October 2007 21:21:59 Tai-Yen Chen wrote:

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hi, Can anyone tell me whether I can use ifeffit to do this job?

I want to know the % change in chi when the molecule have 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 get 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 on.

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 Ifeffit.

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@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: http://cars9.uchicago.edu/~ravel/software/exafs/

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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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