FEFF Program control

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Program control using intermediate output files

In addition to the CONTROL card and other options in ‘feff.inp’, some parameters in the files read by the various modules can be changed. For example, you can create your own paths by editing ‘paths.dat’ and explicitly change Debye–Waller factors in the final result by editing ‘list.dat’.

Users may edit some files as a quick and sometimes convenient way to prepare a given run. It is easiest to use an existing file as a template, since the code that reads these files is fussy about their format.

Using ‘paths.dat’

You can modify a path, or even invent new ones, such as paths with more than the pathfinder maximum of 8 legs. For example, you could make a path to determine the effect of a focusing atom on a distant scatterer. Whatever index you enter for the path will be used in the filename given to the ‘feffNNNN.dat’ file. For example, for the choice of index 845, the EXAFS parameters will appear in ‘feff0845.dat’. A handy way to add a single scattering path of length R is to make a 2-leg path with the central atom at (0, 0, 0) and the scatterer at (R, 0, 0).

GENFMT will need the positions, unique potentials, and character tags for each atom in the path. The angles and leg lengths are printed out for your information, and you can omit them when creating your own paths by hand. The label lines in the file are required (there is code that skips them, and if they’re missing, you’ll get wrong results).

Using ‘list.dat’

This is the list of files that ff2chi uses to calculate chi. It includes the paths written by module GENFMT, curved wave importance factors, and user-defined Debye–Waller factors. If you want to set Debye–Waller factors for individual paths, you may edit this file to set them. FF2CHI will sum the Debye–Waller factors in this file with the correlated Debye model σ2 and the global σ2, if present. You may also delete paths from this file if you want to combine some particular set of paths. (CAUTION: Save the original, or you’ll have to re-run GENFMT!)

Using ‘geom.dat’

This file can be manually edited to take advantage of the paths symmetries.



FEFF Input and Output Files

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