% Copyright (c) 2000 Bruce Ravel % Permission is granted to copy, distribute and/or modify this % document under the terms of the GNU Free Documentation License, % Version 1.0 or any later version published by the Free Software % 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 % modify it under the terms of the GNU Free Documentation License as % published by the Free Software Foundation; either version 1, or (at % your option) any later version. % % You should have received a copy of the GNU Free Documentation License % along with `EXAFS Analysis Using FEFF and FEFFIT'; see the file % COPYING. If not, write to the Free Software Foundation, 675 % Massachusettes Ave, Cambridge, MA 02139, USA. % % Permission is granted to make and distribute verbatim copies of this % manual provided the copyright notice and this permission notice are % preserved on all copies. % % Permission is granted to copy and distribute modified versions of this % manual under the conditions for verbatim copying, provided that the % entire resulting derived work is distributed under the terms of a % permission notice identical to this one. % % Permission is granted to copy and distribute translations of this % manual into another language, under the above conditions for modified % versions, except that this permission notice may be stated in a % translation approved by the author. title = GaN, polarization in plane data = data/perpk.chi out = fits/perp kspout = yes rspout = yes qspout = no kmin = 2 kmax = 12 dk = 1 kw = 1 rmin = 1 rmax = 3.4 format = ascii all = no % bkg = true bkgfile = fits/perpk.background %% This fitting problem is not to much more complicated, at least out %% to the second shell, than copper metal. Three interesting things %% are introduced in this fit: %% 1. polarization: separate feff calulations were run for parallel %% and perpendicular polarization. The appropriate set of %% feffNNNN.dat files are used. %% 2. multiple e0 parameters: this will be discussed in more detail %% when we look at EuTiO3. The basic idea is that we want to %% account for errors in feff's phases which might be element %% specific. Thus an e0 parameter is used for each species of %% back-scatterer. %% 3. path lengths are computed from crystallographic parameters: %% below we set and guess various parameters relating to the %% crystal structure and use math expressions to come with delr %% math expressions. We will discuss this sort of model building %% in much greater detail when we look at PbTiO3. %% %% The main thing to take away from this exercise is that polarized %% data and non-polarized data are handled in the same manner by %% feffit, assuming that feff has made the proper polarized %% calculation. This is much easier and more accurate than using a %% cos^2 rule to modify path amplitudes. %% %% Things to try: %% %% 1. Uncomment the nofit keyword below and run feffit. This will %% tell feffit to read and interpret the input file and all data %% and feff files, but not to run the fit. The log and prm %% files will contain the results of all math expressions %% evaluated with the starting guess values. This is a good way %% to "spell check" math expressions. All delr values should be %% 0 within numerical precision (a few times 10^-5 for feffit, %% depending on the math expression). %% 2. You could try adding higher shells and doing the fit. Beyond %% the second shell GaN is a bit tricky and the data isn't quite %% good enough to properly determine the structure out there. %% Still, it is good to get some practice with MS paths and the %% fit results shouldn't be that bad... %==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+== % nofit set amp 0.93 guess sig_n 0.001 guess sig_ga 0.004 % guess sig_n2 0.001 % guess sig_n3 0.001 set sigmm 0.00042 guess e0n 0.0 guess e0ga 0.0 set ei 0.0 %==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+== set a0 3.190 set delta_a 0 set a a0+delta_a set c0 5.189 set delta_c 0 set c c0+delta_c guess u 0.377 %==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+== s02 0 amp set r_2 sqrt(a**2/3 + ((.5-u)*c)**2) ! N 1st % set r_3 sqrt(a**2/3 + (c/2)**2) ! Ga 2nd %==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+==+== s02 0 e0 0 path 1 feff/perp/feff0001.dat id 1 amp=100.000 deg=1 nlegs=2 reff=1.9372 e0 1 e0n delr 1 u*c - reff sigma2 1 sig_n + sigmm ei 1 ei path 2 feff/perp/feff0002.dat id 2 amp=100.000 deg=1 nlegs=2 reff=1.9462 e0 2 e0n delr 2 r_2 - reff sigma2 2 sig_n + sigmm ei 2 ei path 3 feff/perp/feff0003.dat id 3 amp=100.000 deg=1 nlegs=2 reff=1.9462 e0 3 e0n delr 3 r_2 - reff sigma2 3 sig_n + sigmm ei 3 ei path 4 feff/perp/feff0004.dat id 4 amp=100.000 deg=1 nlegs=2 reff=1.9462 e0 4 e0n delr 4 r_2 - reff sigma2 4 sig_n + sigmm ei 4 ei path 5 feff/perp/feff0005.dat id 5 amp=23.039 deg=2 nlegs=2 reff=3.1690 e0 5 e0ga delr 5 a - reff sigma2 5 sig_ga + sigmm ei 5 ei path 6 feff/perp/feff0006.dat id 6 amp=23.039 deg=2 nlegs=2 reff=3.1690 e0 6 e0ga delr 6 a - reff sigma2 6 sig_ga + sigmm ei 6 ei path 7 feff/perp/feff0007.dat id 7 amp=23.039 deg=2 nlegs=2 reff=3.1690 e0 7 e0ga delr 7 a - reff sigma2 7 sig_ga + sigmm ei 7 ei end path 8 feff/perp/feff0008.dat id 8 amp=71.973 deg=2 nlegs=2 reff=3.1800 delr 8 sigma2 8 path 9 feff/perp/feff0009.dat id 9 amp=71.973 deg=2 nlegs=2 reff=3.1800 delr 9 sigma2 9 path 10 feff/perp/feff0010.dat id 10 amp=71.973 deg=2 nlegs=2 reff=3.1800 delr 10 sigma2 10 !!&& 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 21:09:50 bruce>