[Ifeffit] FEFF calculation for two inequivalent absorbing sites

Eugenio Paris eugenio.paris at gmail.com
Fri Apr 10 08:10:25 CDT 2015

Thank you for your answers,

I think there were several troubles on my analysis.

First of all i didn't understand well how the fuzzy degeneracy works but
after your suggestion i read the JSR paper and now it is pretty clear.
Also, the fact that i was obtaining twice the same path list in the two
sites was due to the mislabeling of the two Co sites (now it works!).

Thank you !


2015-04-09 22:04 GMT+02:00 Bruce Ravel <bravel at bnl.gov>:

> Regarding the "Aggregate" button, it is important to understand what that
> button is trying to do.  It is a tool that is very easy to misuse, or at
> least get confused by.
> You should read this page from the manual:
>    http://bruceravel.github.io/demeter/artug/feff/aggregate.html
> and this article:
>    http://dx.doi.org/10.1107/S1600577514014982
> If it's what you're looking for, cool.
> B
> On 04/09/2015 06:01 AM, Eugenio Paris wrote:
>> Hello everybody,
>> I'm trying to make Co K-edge EXAFS fitting for the Co3O4 compound (*.cif
>> file is attached). The nearest neighbour of Co is oxigen at about 1.93
>> Angstrom distance.
>> Cobalt sits in two inequivalent sites in the unit cell. When I perform
>> the FEFF calculation in Artemis for either one or the other site i get
>> the same path with Reff = 1.93 and degeneracy = 4.
>> So i wonder what is the correct way to take account of the presence of
>> both sites. At the beginning i was thinking to put 2*amp as S0^2
>> parameter to take account for twice the coordination number.
>> Then i tried to use the "Aggregate" option in Artemis. When I use this
>> option i get exactly the same result, i.e. a SS path with Reff = 1.92
>> and degeneracy = 4... I was expecting to get twice the degeneracy.. (the
>> margin and beta parameters are set to default)
>> My question is:
>> Why do i get the same path list when I do use the "Aggregate" pathfinder
>> and when I don't? What is wrong in my interpretation?
>> Thank you in advance!
>> Sincerely,
>> Eugenio
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> --
>  Bruce Ravel  ------------------------------------ bravel at bnl.gov
>  National Institute of Standards and Technology
>  Synchrotron Science Group at NSLS-II
>  Building 535A
>  Upton NY, 11973
>  Homepage:    http://bruceravel.github.io/home/
>  Software:    https://github.com/bruceravel
>  Demeter:     http://bruceravel.github.io/demeter/
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