[Ifeffit] Inequivalent atomic positions (V2O5 xerogel)

Tue Mar 18 12:00:03 CDT 2014

Thaks Anatoly, in fact I have a set of EXAFS data of V2O5 xerogel
intercalated with Co atoms. I would like to have information of the effects
of Co intercalation in the local order around vanadium atoms.

2014-03-18 12:30 GMT-03:00 Anatoly I Frenkel <afrenke2 at yu.edu>:

>  Academically speaking, valid, but, practically, may not be useful if
> your purpose is to fit the data and not just to construct a valid
> theoretical calculation.
> Most likely, the constraints you will have to apply in order to limit the
> number of variables will be too restrictive which will defeat the purpose
> of making such a detailed model.
>
>  Anatoly
>
>
>  Sent from my mobile phone, please forgive typos
>
> ----- Reply message -----
> From: "Douglas Langie da Silva" <douglaslangie at gmail.com>
> To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
> Subject: [Ifeffit] Inequivalent atomic positions (V2O5 xerogel)
> Date: Tue, Mar 18, 2014 11:22 AM
>
>  Thanks guys. With respect to the numbers, I only try a quick fit in
> order to formulate the question in the list. My interest is to know if
> the procedure to consider the two inequivalent positions is valid.
>  Regards.
>
>
> 2014-03-18 11:57 GMT-03:00 Bruce Ravel <bravel at bnl.gov>:
>
>> On 03/18/2014 10:31 AM, Douglas Langie da Silva wrote:
>>
>>>
>>> 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?
>>>
>>
>>  What you have done seems very much like the common explanation for this
>> given by me and others on this list.
>>
>> I'd be a bit worried about the negative sigma^2 and I'd wonder why you
>> are not floating Delta R parameters, but those are details.  The basic
>> answer to your question is, seems valid to me.
>>
>> B
>>
>>
>> --
>>  Bruce Ravel  ------------------------------------ bravel at bnl.gov
>>
>>  National Institute of Standards and Technology
>>  Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
>>  Building 535A
>>  Upton NY, 11973
>>
>>  Homepage:    http://xafs.org/BruceRavel
>>  Software:    https://github.com/bruceravel
>>
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>
>
>
> --
> 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
>
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>

-- 
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
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