[Ifeffit] Fwd: scattering amplitude by FEFF and Artemis

[Bruce Ravel]

Feng,

I am forwarding this to the Ifeffit mailing list since I am in the
middle of an experiment and don't have much time to devote to an
answer. 


> Dear Dr. Ravel,

> I am now learning to use your Artemis program to calculate the scattering 
> amplitude from each paths (shells). It seems your Artemis can give the 
> scattering amplitude of each path, as done by EXAFS calculations in FEFF. I 
> think the results from both program should be same or comparable, but it 
> looks much different, as attached for a result of diamond-K. Is anything 
> wrong with my calculations?

It's really hard to tell.  The figure you sent does not convey any
sense of how it was made.  Without a clear explanation of what you
did or, better yet, an artemis project file to inspect, I am not sure
how I can possibly answer your question.

> I have been wondering how big a cluster we should use for FEFF calculations, 
> or the contributions of the atoms far from the central atom (e.g. > 1nm) 
> since so big clusters (such as 400 atoms and even more) are used for FEFF 
> calculations in several recent publications. I hope to get some ideas from 
> the scattering amplitude of the paths involved by the atoms far from the 
> central atoms. Do you also have any suggestions? 

The nice thing about feff is that it is very easy to use to answer
this sort of question without having to rely on an "expert".  What
happens if you run feff with clusters ranging from very small to very
large and compare the chi(k) functions generated for the first few
coordination shells?

B

> Feng


> ====================================
> EM group, NINT
> 11421 Saskatachewan Drive
> Edmonton, Canada T6G 2M9

-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
 Argonne IL 60439, USA                                fax: (1) 630 252 9793

 My homepage:    http://cars9.uchicago.edu/~ravel 
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/


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