[Ifeffit] Theoretical value of S02 for different absorber

Thu Apr 5 05:44:05 CDT 2012

Dear Dr. Ravel,

Thank you very much for your prompt reply. I followed the instruction on (http://leonardo.phys.washington.edu/feff/wiki/index.php?title=EXAFS_calculation) and activated S02 card by making S02 0.0 in feff.inp file. As a result, FEFF calculated S02.

However, I get confused when I compare FEFF calculated S02 with reported value in literature and the one obtained from my own fit.

For example,

S02 for Mn absorber

FEFF calculated                           0.94
Fitted value for my sample               ~0.75
Fitted value for various Mn-oxides       ~0.75
Other reported value from Mn fit         ~0.70-0.80 (http://www.sciencedirect.com/science/article/pii/S0020169397057496)

S02 for Fe absorber

FEFF calculated                          ~0.94
Fitted value for Fe-foil                 ~0.70
Fitted value for various Fe-oxides       ~0.70
Reported value by calculation             0.69 (http://prola.aps.org/abstract/PR/v169/i1/p27_1)

It is well known that S02 is a property of central absorbing atom and is considered to be constant between 0.7 - 1.0. However, in real world, S02 is affected by various systematic errors like thicker samples (in transmission), absorption by other elements in sample at given energy range and many more. These factors can suppress the amplitudes of EXAFS oscillations resulting in lower value of fitted S02 than it should be for a given absorber.

The reason I am so much curious about S02 is, if I know what should be (or should be considered) the value of S02 for a given absorber than I can possibly understand the reasons of fitted S02 being too low or too high. For instance, S02 and Sigma2 are highly correlated for first shell. So from fitted value of S02 and Sigma2 of first shell, I could possibly understand changes in local structure.

So I would like to put forward very simple but still confusing question that which value of S02 should be considered, FEFF calculated or the one obtained by fitting standards (either reference foils or reference compounds measured on same beamline) and why.

Many thanks in advance !!!

With best regards,
Jatin

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Today's Topics:

   1. Theoretical value of S02 for different absorber (Jatin Rana)
   2. Re: Theoretical value of S02 for different absorber (Bruce Ravel)

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Message: 1
Date: Wed, 4 Apr 2012 17:45:13 +0800 (SGT)
From: Jatin Rana <jatin_rana2002 at yahoo.com>
To: "ifeffit at millenia.cars.aps.anl.gov"
        <ifeffit at millenia.cars.aps.anl.gov>
Subject: [Ifeffit] Theoretical value of S02 for different absorber
Message-ID:
        <1333532713.14873.YahooMailNeo at web193501.mail.sg3.yahoo.com>
Content-Type: text/plain; charset="utf-8"

Dear Ifeffit users,

Can anyone recommend a reference where I can get calculated value of S02 for various elements ? I would like to compare them with my fitted values.

Many thanks in advance !!

With best regards,
Jatin Rana
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Message: 2
Date: Wed, 4 Apr 2012 08:19:34 -0400
From: Bruce Ravel <bravel at bnl.gov>
To: Jatin Rana <jatin_rana2002 at yahoo.com>,      XAFS Analysis using Ifeffit
        <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Theoretical value of S02 for different absorber
Message-ID: <201204040819.35087.bravel at bnl.gov>
Content-Type: Text/Plain;  charset="iso-8859-15"

On Wednesday, April 04, 2012 05:45:13 am Jatin Rana wrote:
> Dear Ifeffit users,
>
> Can anyone recommend a reference where I can get calculated value of S02
> for various elements ? I would like to compare them with my fitted values.

http://leonardo.phys.washington.edu/feff/wiki/index.php?title=EXAFS_calculation

--

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter

------------------------------

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