[Ifeffit] Debye Waller factors for Water Molecules

[Frenkel, Anatoly]

Paul and Shelly,
 
I do not think Einstein temperature for Zn-S bond should be recycled as the Einstein temperature for a Zn-O bond. To my opinion, the best approximation for Zn-O Einstein temperature would be to look up for EXAFS data on Zn2+ complexes in aqueous solution, assume that what they publish for sigma2 is dominated by thermal disorder, and calculate Einstein temperature for Zn-O from the published value of sigma2. Then, extrapolate the sigma2 to low temperature by an Einstein model. That would probably give a lower bound of the total disorder in Zn-O that you expect for this bond in your complex, since some static disorder may be present as well.
 
Anatoly

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From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of Kelly, Shelly D.
Sent: Fri 7/27/2007 8:55 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Debye Waller factors for Water Molecules



Hi Paul,

 

I was hoping someone else would answer your question.  I have an idea. It might not be a good idea.  

 

Look up the MSRD term that you get from Grant's DFT parameterizations for the first Zn-S bond.  Play around with the Einstein model for a Zn-S bond of the correct distance for the first Zn-S bond, to determine the correct Einstein temperature that gives the MSRD value that you looked up from Grant's DFT.  Then use that Einstein temperature and the Einstein model for the Zn-O bond of the water molecule.

--It might work....

 

Cheers,

Shelly

 

 

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From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Paul Fons
Sent: Thursday, July 26, 2007 9:29 PM
To: XAFS Analysis using Ifeffit
Subject: [Ifeffit] Debye Waller factors for Water Molecules

 

  I am analyzing some Zn organo-metallic protein complexes and have take EXAFS data at low temperature at the Zn edge.  I am now in the midst of trying to fit the data.  For the mean squared relative displacement terms, I am using Grant's DFT parameterizations for the Zn-cysteine system.  This is working fine.  In one of my complexes, I also have a water molecule within the "first shell".  Does anyone have a suggestion for a reasonable MSRD term for this (at 20 K)?

 

                                                Paul

 

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