%       Copyright (c) 2000 Bruce Ravel
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%       Foundation; with the Invariant Sections being "EXAFS Analysis
%       Using FEFF and FEFFIT, Part 1: Presentation", "EXAFS Analysis
%       Using FEFF and FEFFIT, Part 2: Commentary", and all related
%       analysis examples, with no Front-Cover Texts, and with no
%       Back-Cover Texts.  A copy of the license is included in the
%       section entitled "GNU Free Documentation License".
% 
% 
% This file (and all files associated with `EXAFS Analysis Using FEFF
% and FEFFIT') are free documentation; you can redistribute it and/or
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title = AgBr(0.5)Cl(0.5)
data = data/abc20k.chi
out = fits/abc20
kmin = 2	kmax = 14	dk = 1	kw = 1
rmin = 1.3	rmax = 3
formin = ascii	all = no	cormin = 0.5
rspout = yes	qspout = yes	kspout = yes

bkg = false
bkgfile = fits/abc20k.background

%% common parameters
guess	amp		0.9		%% S0^2
set	sigmm		0.00018		%% normalization correction
guess	x		0.5		%% mixing parameter

%% Here I have created the simplest possible structural model.  I
%% simply allow the parameters of the exafs equation to float freely
%% for each kind of scatterer.  This produces decent results but
%% doesn't really use the data very well.  One could:
%%
%%   1. Fit shells beyond the first shell (these data are quite good
%%      enough for that!).  Including the third shell will help refine
%%      x.
%%
%%   2. Fit or co-refine several temperatures (note that the x
%%      parameter HAS to be independent of x at sufficiently low
%%      temeprature and assuming random dissolution of Cl) 
%%
%%   3. Measure the Br edge and co-refine it with the Ag edge.
%%      (Unfortunately, I only have one scan Br edge data at 20K).
%%      This is a very useful thing to do because you can come up with
%%      a structural model that describes the 3-d distorted structure
%%      of the mixed material.  Then compute delr parameters from the
%%      parameters in this fancy model.  The two edges must measure
%%      the same thing, so the fancy parameters are common to both
%%      edges.  Cool!

%% Bromine parameters
guess	e0_br		0.0
guess	sig1_br		0.003
guess	dr_br		0.0

%% Chlorine parameters
guess	e0_cl		0.0
guess	sig1_cl		0.003
guess	dr_cl		0.0


path	1	feff/feff0001.dat
id	1	first shell Br
s02	1	(1-x)*amp
e0	1	e0_br
delr	1	dr_br
sigma2	1	sig1_br + sigmm

path	2	feff/cl1/feff0001.dat
id	2	first shell Cl
s02	2	x*amp
e0	2	e0_cl
delr	2	dr_cl
sigma2	2	sig1_cl + sigmm

end

%% Here are some more shells to play with:

path	3	feff/feff0002.dat
id	3	second shell Ag
s02	3	amp
e0	3	e0_ag
delr	3	dr_ag2
sigma2	3	sig1_ag2 + sigmm

path	4	feff/feff0005.dat
id	4	third shell Br
s02	4	(1-x)*amp
e0	4	e0_br
delr	4	dr_br3
sigma2	4	sig1_br + sigmm

path	5	feff/cl1/feff0005.dat
id	5	third shell Cl
s02	5	x*amp
e0	5	e0_cl
delr	5	dr_cl3
sigma2	5	sig1_cl3 + sigmm

%% The next shell involves MS paths.  The x parameter must be
%% considered in the MS paths since there is scattering through the
%% Br/Cl site.  Depending on the complexity of your structural model,
%% you might need to consider non-collinear scattering angles as well.
%% Since this is a structurally disordered material, the paths at the
%% fourth shell distance are probably very hard to measure at elevated
%% temperature.

!!&& Local Variables:
!!&& input-out-path: "fits/"
!!&& input-feff-path: "feff/"
!!&& input-data-path: "data/"
!!&& input-program-name: "feffit"
!!&& End:
%# Input-mode Time-stamp: <2000/03/11 21:02:54 bruce>