[Ifeffit] how to reduce the core-hole lifetime broadening in feff8.2

joshua jason kas hebhop at u.washington.edu
Fri Jun 12 13:28:47 CDT 2009

> And yet, the documentation for the CORRECTIONS keyword says:
>   "The real energy shift vrcorr moves E0 in the final \chi(k) and
>    the imaginary energy shift vicorr adds broadening to the
>    result. The real energy shift is useful to correct the error in
>    FEFF's Fermi level estimate and the imaginary part can be used to
>    correct for experimental resolution or errors in the core-hole
>    lifetime."
> And a couple of sentences later:
>   "The imaginary energy is typically used to correct for instrument
>    broadening or as a correction to the mean free path calculated by
>    feff."
> Perhaps the document should be updated to explain more clearly what
> CORRECTIONS actually does.
Thank you Bruce. I will try to clear up the documentation. Let me state 
more clearly how these two cards can be used to change the broadening of 
the spectrum. In the EXCHANGE card, the user can use negative values to 
offset the core hole broadening. The CORRECTIONS card can only be used to 
add to the total (previous) broadening, which is given by the half width 
at half max,
 	Gamma_CH/2 + vi, 
where vi is the broadening from the EXCHANGE card and Gamma_CH is the 
core hole broadening.
The benefit of using the CORRECTIONS card is that it is very fast since 
you can skip the matrix inversion for the FMS calculation. Thus a good way 
to use the two cards together is to reduce the broadening via EXCHANGE 
by a bit too much (use an overestimate as a first try), then use the 
CORRECTIONS card to fine tune the broadening.
> Bruce Ravel  ------------------------------------ bravel at bnl.gov
> National Institute of Standards and Technology
> Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
> Building 535A
> Upton NY, 11973
> My homepage:    http://xafs.org/BruceRavel
> EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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> End of Ifeffit Digest, Vol 76, Issue 8
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