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3. Program and file structure

This section describes the files and data used by the various modules. The main program FEFF reads one file created directly by the user, the file feff.inp; it is line oriented with a KEYWORD in CAPITAL LETTERS followed by data in free format. Tab characters are NOT permitted (due to portability constraints). Comments may be added at the end of any line after any required data, and spaces between lines are ignored. Any line beginning with an asterisk (*) is a comment and is ignored. An auxilliary program is provided which generates the feff.inp file from crystallographic input parameters.

Other files required by the various modules are created by FEFF from feff.inp. Some of these other files may be edited by the user as a way to modify the input data to the modules, see section 5. See the PRINT card in section 4 to obtain various diagnostic files. Table 3.1 summarizes this structure, the rest of this section describes the structure in more detail.

3.1 Table 3.1

module  input files     output files    other useful output
------  -----------     ------------    -------------------
POTPH   feff.inp        phase.bin       diagnostic files
        potph.inp       xsect.bin       (see PRINT card)

PATHS   feff.inp        paths.dat       crit.dat

GENFMT  feff.inp        files.dat
        phase.bin       feffNNNN.dat

FF2CHI  feff.inp        chi.dat         chipNNNN.dat
        files.dat       xmu.dat 

3.2 Scattering potential and phase shift code, POTPH

Reads potph.inp, which is created by FEFF's input routine from feff.inp. potph.inp is deleted by FEFF after use. POTPH writes the binary file phase.bin, which contains the scattering phase shifts and other information needed by PATHS and GENFMT. If the XANES card is used, POTPH will print the cross-section data in xsect.bin. Optionally, POTPH will write other diagnostic files with information about the potentials and phase shift calculations.

3.3 Path enumeration, PATHS

Reads geom.dat, which is created by FEFF from the information in feff.inp, and phase.bin. geom.dat is deleted after use unless explicitly saved (see PRINT card). PATHS writes paths.dat for use by GENFMT and as a complete description of each path for use of the user. PATHS will optionally write other diagnostic files. The file crit.dat is particularly useful when studying large numbers of paths. When studying large numbers of paths, this module will optionally write only crit.dat and save geom.dat, not writing paths.dat.

3.4 Scattering amplitude and other XAFS parameter calculation, GENFMT

GENFMT reads phase.bin and paths.dat, and writes a file feffNNNN.dat for each path, where NNNN is the 4-digit path number taken from paths.dat. The feff.dat files contain the XAFS parameters for each path and can be used by FF2CHI, or can be used directly by other programs. These files are the main output of FEFF. The file files.dat is a list of these filenames with the importance of each path.

3.5 XAFS spectrum calculation, FF2CHI

FF2CHI reads files.dat, reads the files listed and files.dat and writes chi.dat with the total XAFS from these files. Additional instructions are passed to FF2CHI from feff.inp, so you can change S02, Debye temperature and some other parameters without re-doing the whole calculation. The file files.dat can be edited by hand to change the files being considered, and individual chipNNNN.dat files with chi from each path are optionally written. If the XANES card is specified and xsect.bin exists, FF2CHI will write the XANES data in xmu.dat.

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