Inequivalent atomic positions (V2O5 xerogel)
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
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
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
<Model v1.jpg> <Model v2.jpg> _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Thanks Chris. Regards.
2014-03-18 11:54 GMT-03:00 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@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
<Model v1.jpg> <Model v2.jpg> _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- 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
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@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
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
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@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
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- 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
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"
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
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"
To: "XAFS Analysis using Ifeffit" 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
: 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@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
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- 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
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- 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
Hi Douglas: On Tue, 18 Mar 2014, Douglas Langie da Silva 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?
This is the right way to fit these inequivalent sites as others have mentioned. The biggest question is what are you trying to learn about this material? Depending on your answer, I would modify the model to extract the important information. The challenge you have in this data is that you have 8 paths and a very limited number of free parameters. It looks like you have chosen to allow the E0, S02, and sigma^2 to vary. A different selection of variable parameters might suit your goals better. Carlo -- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org
I think it is not valid. You have too many fitting parameters for the first shell (all your sigma2 are independent variables) and you ran out of independent points that are limited by the delta R and delta K. To increase delta R you extended your fitting range to the second shell but is cheating because your theory does not account for the second peak. You should try to make sigma2 constant, or try a Debye model, or, better, use the following approach. Make a histogram of all 10 distances that are present in the structure between V and O. See if the histogram is more or less symmetric. If it is, use a representative path that is close to the middle distance from the histogram and assign CN =5, and effective sigma2 (that will include both dynamic and configurational components). Also. Include delta R for that path. Then you will have a chance. Anatoly Sent from my iPad
On Mar 18, 2014, at 10:44 AM, "Douglas Langie da Silva"
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
<Model v1.jpg> <Model v2.jpg> _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
participants (5)
-
Anatoly I Frenkel
-
Bruce Ravel
-
Carlo Segre
-
Chris Patridge
-
Douglas Langie da Silva