Re: [Ifeffit] Fwd: scattering amplitude by FEFF and Artemis
Thank you, Dr. Ravel, Could you please just simply tell me the expression for the magnitude of chi (q) (labelled as |chi(q)|)? Thank you. Feng
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@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/
==================================== EM group, NINT 11421 Saskatachewan Drive Edmonton, Canada T6G 2M9
Dear Feng,
On 6/28/07, Feng Wang
Thank you, Dr. Ravel,
Could you please just simply tell me the expression for the magnitude of chi (q) (labelled as |chi(q)|)? Thank you.
I'm sure you didn't mean to sound so demanding, but perhaps you would consider following Bruce's suggestion of sending a project file. For what it's worth (in case you missed it while you were reading the docs and tutorials), |chi(q)| = magnitude of the complex chi(q) = FT^(-1) [ chi(R) * Window(R) ] where Window(R) is a Windowing function and chi(R) = FT[ chi(k) * k^w * Window(k) ] where Window(k) is a Windowing function and w is the k-weighting. Both FT's are band-limited (Rmin,Rmax, and kmin,kmax, respectively). The convention used in Ifeffit is that chi(k) is strictly real. This isn't particularly important if you're only interested in the magnitude. I thought your original question was about scattering amplitudes.... Are these questions related? I couldn't tell much from the plot you sent, as I didn't understand what "X Axis Title" or "Y Axis Title" were meant to represent. Of course, the "scattering amplitude" f(k) is not the only factor setting the amplitude of chi(k). Hope that helps. If not, please let us know what the issue is, --Matt
participants (2)
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Feng Wang -
Matt Newville