On 03/18/2014 10:31 AM, Douglas Langie da Silva wrote:What you have done seems very much like the common explanation for this given by me and others on this list.
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?
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
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