[Ifeffit] S02 and k_min

Morrill, Michael R mike.morrill at gatech.edu
Mon Dec 3 22:49:37 CST 2012


Thank you for your replies, Anatoly and Matt. As suggested, I've attached a zipped folder with 2 fits that differ only in kmin. You'll notice that the fit improves as kmin is increased. I've also attached the raw data in an Athena file in the event that anyone would like to look at that.

Thanks again.

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Subject: Ifeffit Digest, Vol 118, Issue 2

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Today's Topics:

   1. Re: S02 and k_min (Anatoly I Frenkel)
   2. Re: S02 and k_min (Matt Newville)


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Message: 1
Date: Sun, 2 Dec 2012 18:13:14 +0000
From: Anatoly I Frenkel <afrenke2 at yu.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] S02 and k_min
Message-ID:
	<545F89325F51764C902D37B42C9F4D5313625DAE at YUWEXCPM12.yuad.uds.yu.edu>
Content-Type: text/plain; charset="us-ascii"

Michael,

If you use the same  kmin for the standard and the unknown you will minimize the ambiguity.

Anatoly


----- Reply message -----
From: "Michael Morrill" <mike.morrill at gatech.edu>
To: "ifeffit at millenia.cars.aps.anl.gov" <ifeffit at millenia.cars.aps.anl.gov>
Subject: [Ifeffit] S02 and k_min
Date: Sun, Dec 2, 2012 1:02 PM



Hello everyone,

I am currently performing a simple curve fit on bulk MoS2 using an atoms file for crystalline MoS2. I've found that increasing k_min on my fit (e.g. from 2 to 4) improves the quality of the fit (R-factor from 0.028 to 0.009), but also increases S02. If I use a large enough k_min (but not so large I run out of data), S02 gets as high as 1.2 +/- 0.05. This trend is observable for single and multiple k-weight fittings.

While I understand that S02>1.0 does not necessarily invalidate the fit, I am not sure how to justify which parameter values are the best seeing that "0.8<S02<1.0" is often one of the justifications that everything "is reasonable." Ultimately, I want to assume the S02 is chemically transferrable and use it for curve fits on metal oxide supported MoS2.

Any direction on the mater would be greatly appreciated.

Thank you,
Mike Morrill
GaTech CHBE
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Message: 2
Date: Sun, 2 Dec 2012 12:58:58 -0600
From: Matt Newville <newville at cars.uchicago.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] S02 and k_min
Message-ID:
	<CA+7ESbqKeaqjKnF6M8w0QDuepaZCEM=_xLFgLDg2cQOQsA0QAQ at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Hi Mike,

On Sun, Dec 2, 2012 at 11:54 AM, Michael Morrill
<mike.morrill at gatech.edu> wrote:
> Hello everyone,
>
> I am currently performing a simple curve fit on bulk MoS2 using an atoms file for crystalline MoS2. I've found that increasing k_min on my fit (e.g. from 2 to 4) improves the quality of the fit (R-factor from 0.028 to 0.009), but also increases S02. If I use a large enough k_min (but not so large I run out of data), S02 gets as high as 1.2 +/- 0.05. This trend is observable for single and multiple k-weight fittings.
>
> While I understand that S02>1.0 does not necessarily invalidate the fit, I am not sure how to justify which parameter values are the best seeing that "0.8<S02<1.0" is often one of the justifications that everything "is reasonable." Ultimately, I want to assume the S02 is chemically transferrable and use it for curve fits on metal oxide supported MoS2.
>
> Any direction on the mater would be greatly appreciated.

I think you'll get more useful replies if you can provide a simple
project file that shows the effect.

--Matt



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