[Ifeffit] extract backscattering amplitude and phase shift files after feff calculation

Bruce Ravel bravel at bnl.gov
Fri Sep 5 12:24:06 CDT 2014

On 09/05/2014 10:18 AM, Matthias Filez wrote:
> Dear mailing list user,
> I would like to obtain the backscattering amplitude and phase shift
> files, generated during feff calculations, for photo-electron paths used
> during modelling. These files (containing F(k), j(k)) should be located
> in some directory but I really cannot find them back.
> I know this question has been asked before, but no conclusive answer was
> provided. I use Windows 7, Intel(R) Core(TM) i5-2520M CPU @ 2.5 GHz,
> 64-bit OS, 4 GB RAM. Currently I employ Demeter 0.9.13.
> Please provide me your suggestions/solutions,
> Many thanks in advance,
> Matthias Filez

Hi Matthias,

I purposefully designed Artemis to hide the feff calculation from the
user.  That is, I wanted the user to be thinking about what the path
*is* rather than how it is represented on disk.  While it certainly is
possible to find the relevant files while using Artemis, it's non
trivial and they have been renamed in a way that is convenient for the
computer, but not so much for the human.

I think the easiest thing for you to do is to run feff by hand.  That
is, save the feff.inp file and run feff from the command line.  There
is a feff6 executable in C:\strawberry\c\bin\feff6.exe.  (You might
also consider upgrading Demeter, 0.9.13 is somewhat old.)

Doing so will write out a pile of files called "feffNNNN.dat", where
"NNNN" is the path index and the paths are sorted by half path length.
Typically 0001 is the first shell SS path.

The columns in feffNNNN.dat are not exactly what you are looking for,
but they are close.  Here's what the feff6 document has to say about
the content of those files:


The second link is not formatted in a very friendly way, but does
explain how to turn the columns of the feffNNNN.dat file into the
quantities you want.

Larch has functionality that substantially simplifies interacting with
the feffNNNN.dat files, including providing easy access to the arrays
that you are asking about:


I am not certain why you think that there is no conclusive answer to
the question of how to access information about specific scattering
paths.  It's all fairly well documented and you can, of course, read
the source code of feff, ifeffit, or larch to see how its done.
Perhaps you are looking to do something beyond what you I presumed
from your email....?

Source code:
   feff6: https://github.com/newville/ifeffit/tree/master/src/feff6
   feff8: https://github.com/xraypy/feff85exafs
   ifeffit: https://github.com/newville/ifeffit
   larch: https://github.com/xraypy/xraylarch


  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
  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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