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Input File Controls


 

The main program FEFF reads only one file created directly by the user, the file 'feff.inp' and executes the various program modules described below. An auxiliary program (ATOMS), developed by Bruce Ravel, is provided which can generate the 'feff.inp' file from crystallographic input parameters. Information about ATOMS can be found on the WWW at

This section describes 'feff.inp' and the commands that tell FEFF what to do. It may be helpful to look at one or more of the sample input files in Section 4 while reading this section. The input file for FEFF8 is similar to FEFF version 5 through 7, except that several additional options have been added to permit self-consistent potential generation, full multiple scattering XANES calculations, polarization dependence, and others listed in Section 2.1.

The input file 'feff.inp' is a loosely formated, line oriented text file. Each type of input read by the program is on a line which starts with a card or keyword in CAPITAL LETTERS and, in some cases, is followed by alpha-numeric data. All card arguments listed below inside square brackets are optional. The sequence of keyword cards is arbitrary. If any card or optional data is omitted, default values are used; an exception is the POTENTIALS card, which is always required. Alpha-numeric values are listed in free format, separated by blanks. Tab characters are not allowed (due to Fortran 77 portability constraints) and may cause confusing error messages. Any characters appearing after the card and any required or optional data on a given line are ignored by FEFF and can be used as end-of-line comments. All distances are in Ångstroms and energies in eV. Spaces between lines (empty lines) are ignored. Any line beginning with an asterisk (*) is regarded as a comment and is also ignored.

After reading the 'feff.inp' file, the calculations are done sequentially in six steps:

  1. The scattering potentials are calculated using atomic overlap (Mattheiss) prescription or self-consistently using an automated SCF loop. Absolute energies are estimated. (module POT, potentials).
  2. The scattering phase shifts, dipole matrix elements, x-ray cross-section and angular momentum projected density of states (LDOS) are calculated. (module XSPH, cross-section and phases).
  3. Full multiple scattering XANES calculations are done for a specified cluster size. (module FMS, full multiple scattering).
  4. The leading multiple scattering paths for the cluster are enumerated. (module PATHS).
  5. The effective scattering amplitudes tex2html_wrap_inline3195 and other XAFS parameters are calculated for each scattering path. (module GENFMT, general-path F-matrix calculation).
  6. The XAFS parameters from one or more paths are combined to calculate a total XAFS or XANES spectrum. (module FF2CHI, scattering amplitude to chi).

This section describes how to control each module them using the 'feff.inp' file.



 
next up previous contents
Next: Complete list of FEFF8 Up: No Title Previous: Synopsis
John J. Rehr
Thu Jul 1 14:31:17 PDT 1999