[Ifeffit] (no subject)

[Bruce Ravel]

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 at bnl.gov

 National Institute of Standards and Technology
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