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5. Chapter 5: Run Control Options

In addition to the CONTROL card and the FEFF 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 change explicit Debye-Waller factors in the final result by editing files.dat.

Users may edit the 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 -- these files are read by a computer program that is fussy about what it receives.

The files that can be used in this way are paths.dat and files.dat.

5.1 Paths.dat

You can modify a path, or even invent new ones. 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; i.e., for the choice, index = 845, the exafs parameters will appear in feff845.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).

5.2 Files.dat

This is the list of files that ff2chi uses to calculate chi. It includes the filenames of the feffNNNN.dat files 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 use the Debye-Waller factors in this file unless you have asked to use the correlated Debye model. You may also delete file names from this file if you want to combine some particular set of paths. (Save the original, or you'll have to re-run GENFMT!)

You may re-name the feffNNNN.dat files as long as you remember to change the filenames in files.dat when you want to calculate the XAFS using FF2CHI.


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