[Ifeffit] help: can I use ifeffit to predict chi?
Matthew Marcus
mamarcus at lbl.gov
Fri Nov 2 13:20:07 CDT 2007
I have sent Chen some data on magnetite and maghemite.
mam
----- Original Message -----
From: "Tai-Yen Chen" <tychen at mail.chem.tamu.edu>
To: <bravel at bnl.gov>; "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
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!!
>
>
>
>
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>
>
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>
> 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
>>>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 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:
>>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
>
> Visit us on the web at http://www.chem.tamu.edu
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