could you tell me how does one tune the bond angles from the multiple scattreing paths? Bindu Dr.Bindu R. Visiting Scientist DCMP&MS Tata Institute of Fundamental Research Homi Bhabha Road Colaba Mumbai-400 005 India Mobile-919892536830 --------------------------------- Chat on a cool, new interface. No download required. Click here.
On Tuesday 27 November 2007 09:12:33 Bindu R. wrote:
could you tell me how does one tune the bond angles from the multiple scattreing paths?
Hi Bindu, I don't quite understand the question. Perhaps you can offer a few more details about what you are trying to do.... Are you doing EXAFS analysis considering these MS paths? Are you trying to explore the effect of bond angles on your XANES calculations? B -- Bruce Ravel ----------------------------------- bravel@bnl.gov National Institute of Standards and Technology Synchrotron Measurements Group, Beamlines X23A2, X24A, U7A Building 535A, Room M7 Brookhaven National Laboratory Upton NY, 11973, USA My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
As I understood he wants to measure angles from multiple scattering... do it by calculation taking the known values of multiple and single scattering path... darek
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Bruce Ravel Sent: Tuesday, November 27, 2007 3:20 PM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] (no subject)
On Tuesday 27 November 2007 09:12:33 Bindu R. wrote:
could you tell me how does one tune the bond angles from the multiple scattreing paths?
Hi Bindu,
I don't quite understand the question. Perhaps you can offer a few more details about what you are trying to do.... Are you doing EXAFS analysis considering these MS paths? Are you trying to explore the effect of bond angles on your XANES calculations?
B
-- Bruce Ravel ----------------------------------- bravel@bnl.gov
National Institute of Standards and Technology Synchrotron Measurements Group, Beamlines X23A2, X24A, U7A
Building 535A, Room M7 Brookhaven National Laboratory Upton NY, 11973, USA
My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Hi Bindu: I am presuming that you mean that you want to tune the bond angle of the MS paths in your EXAFS fitting but, as Bruce notes, I might be wrong. The bond angles for the multiple scattering paths are simply calculated from the positions of the atoms around the central atom in the FEFF input file. In the refinement process used by Ifeffit, the overall path length is slightly changed to fit the experimental data. This implies that a 3-Dimensional geometry has been reduced to a 1-Dimensional fitting and all angular information is locked into the initial FEFF calculation. Thus you can only tune angles by starting with a different local arrangement of atoms around the central atoms. To my knowledge, there is no automatic way of doing this but there are manual ways of approaching the problem depending on the kind of system you are studying. It would be helpful to have more information. Cheers, Carlo On Tue, 27 Nov 2007, Bindu R. wrote:
could you tell me how does one tune the bond angles from the multiple scattreing paths?
Bindu
Dr.Bindu R. Visiting Scientist DCMP&MS Tata Institute of Fundamental Research Homi Bhabha Road Colaba Mumbai-400 005 India Mobile-919892536830
--------------------------------- Chat on a cool, new interface. No download required. Click here.
-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://www.iit.edu/~segre segre@debian.org
On Tuesday 27 November 2007 09:33:20 Carlo Segre wrote:
The bond angles for the multiple scattering paths are simply calculated from the positions of the atoms around the central atom in the FEFF input file. In the refinement process used by Ifeffit, the overall path length is slightly changed to fit the experimental data. This implies that a 3-Dimensional geometry has been reduced to a 1-Dimensional fitting and all angular information is locked into the initial FEFF calculation. Thus you can only tune angles by starting with a different local arrangement of atoms around the central atoms.
To my knowledge, there is no automatic way of doing this but there are manual ways of approaching the problem depending on the kind of system you are studying. It would be helpful to have more information.
Carlo is right. There is no automated way of doing so with Feff and Ifeffit at this time. (This is one of the many things I am working towards with my Demeter effort, but that is quite a ways off and is a topic for a different email message.) There are a number of ways of approaching the problem within the context of Feff and Ifeffit. One that I came up with is discussed in Chapter 9 of this thing that I wrote several years ago: http://cars9.uchicago.edu/~ravel/talks/course/notes.pdf. Way back when, Anatoly came up with a somewhat different approach for his work on mixed salts. I think this is the right reference: Solid State Commun., 99, 67 (1996). I am sure Anatoly will pipe up if I got that wrong. Also way back when, Dani Haskel came up with yet another approach. This one appears to be the correct reference: Phys. Rev. B 61, 7055 (2000). Look also at his other papers on the structure of the lanthanum copper oxides. Finally, you might find my paper on barium tantalum oxinitride relevant: Physical Review B73, p. 184121 (2006). HTH, B -- Bruce Ravel ----------------------------------- bravel@bnl.gov National Institute of Standards and Technology Synchrotron Measurements Group, Beamlines X23A2, X24A, U7A Building 535A, Room M7 Brookhaven National Laboratory Upton NY, 11973, USA My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
participants (4)
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Bindu R. -
Bruce Ravel -
Carlo Segre -
Zajac, Dariusz