[Ifeffit] Inequivalent atomic positions (V2O5 xerogel)

[Chris Patridge]

Hello,

I think it is valid. The model for v2o5 is tough to fit well at low R because the apical oxygen bond is so short that there is some significant overlap between the background and signal near 1 angstrom. 

Chris

********************************************
Dr. Christopher Patridge
Assistant Professor of Chemistry
Math and Natural Science Dept
BFAC 009
D'Youville College
320 Porter Ave., Buffalo, NY 14150
716-829-8096

Sent from my iPhone

> On Mar 18, 2014, at 10:31 AM, Douglas Langie da Silva <douglaslangie at gmail.com> wrote:
> 
> Dear all, 
> 
> I am working with EXAFS data of V2O5 xerogel. In this form, the V2O5 present a monoclinic structure formed by bi-layers of VO5 pyramids intercalated with water molecules. Fig 1 attached presents a view of the V2O5 xerogel structure. There are two Vanadium atoms per unit cell, each one surrounded by oxygen atoms at distinct distances, characterizing two inequivalent sites. 
> My question is how to fit the data in dartemis considering the two inequivalent positions? 
> 
> My first approach was run Feff two times. Then I get two theoretical models, one for V1 atoms and the other for the V2 atoms. Each of Feff runs are present attached as model V1 and model V2. After that I transfer the paths of the first shell of each model to dartesmis data windows (fig 2) and proceed with the fit. We pay attention in the site fraction of each vanadium atom in order to setup the S02 parameter for each model.  Without attempting at this point with the numbers, the final results are present in Fig. 3 e 4. Fig 4 presents the log file and the results for the each patch. 
> 
> My question is: this procedure is valid? 
> 
> Since now thak you.    
> 
> -- 
> Douglas Langie da Silva
> Instituto de Física e Matemática
> Departamento de Física
> Universidade Federal de Pelotas
> Campus Universiário s/n
> CP 354
> Pelotas/RS
> CEP 96010-900
> 55 53 32757477
> 55 53 32757345
> 
> Douglas Langie da Silva
> Physics Department
> Federal University of Pelotas
> POBox 354
> Pelotas/RS
> ZCode 96010-900
> 55 53 32757477
> 55 53 32757345
> <Rav 1.jpg>
> <Model v1.jpg>
> <Model v2.jpg>
> <Fig 3.jpg>
> <Fig 4.jpg>
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