Download Appendix A: DND-CAT BEAMLINE PROCEDURES

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where SO2, delR, and sigma2 are all possible FEFFIT fitting parameters and p’ and p”
are the real and imaginary components of the photoelectron momentum. Amp and
Phase are the amplitude and phase functions as calculated by FEFF.
Typically, fitting data is divided into two sections. The first is calibration of the FEFF
data to standard compounds. For example, before trying to fit an unknown sulfur
2
containing zinc compound, the S0 and e0 parameters from a known zinc sulfide should
be fit first. This will greatly reduce the number of variables when fitting the unknown,
2
and helps remove the co-dependence of the coordination number and S0 . Once these
parameters are determined from the known standard, these values are held constant and
the remaining parameters determined for the unknown samples. In addition to several
data files that show the fitting result in k-space and R-space, a feffit.out file summarizes
the numerical results. A sample script for the standardization of parameters for zinc
sulfide is found below.
%
data
out
%
rmin
kmin
dk
%
= /usr/users/swebb/chis/aps1121/zns_t-k.chi
= result.dat
= 1.1
= 2
= 2
rmax = 2.6
kmax = 14
kweight = 3
qspfit = true
set n1 = 4
guess
guess
guess
guess
%
Path
e0 = -9
S02 = 1
sigma2 = 0.001
delr = 0
1
/usr/users/swebb/feff/zn-s/feff0001.dat