Re: Absolute x-ray absorption cross sections with FEFF

["John J. Rehr" <jjr@leonardo.phys.washington.edu>]

Dear Feff users:

 A frequently asked question is whether FEFF yields absolute cross sections
and/or how to get this. FEFF can yield absolute cross-sections, but to get
them, one has to make use of the normalization factor printed out in the header
of the xmu.dat file. This value is calculated at 50 eV above the edge
to avoid the sharp structure close to the edge. For example, look at a recent
xmu.dat file:

Cu crystal, 4 shells                                             
 Abs   Z=29 Rmt= 1.410 Rnm= 1.457 K  shell
 Pot 1 Z=29 Rmt= 1.361 Rnm= 1.399
 Gam_ch=1.729E+00 H-L exch
 Mu=-3.247E+00 kf=1.830E+00 Vint=-1.600E+01 Rs_int= 1.982
 S02  1.000  Temp  190.00  Debye temp  315.00  Global sig2  0.00000
 xsedge+50, used to normalize mu           2.4592E-04
                                           ^^^^^^^^^^ 
                                           normfactor

 Thus the absolute cross section in Ang**2 is  mu = xmu * normfactor
(1 Ang**2 = 100 Mbarn).  For other details see the Absolute cross-section
section of the FEFF document.

  J. Rehr