The input for fcf is keyword oriented and is read from the standard input. fcf recognizes several keywords, but only two have to be specified to perform the calculation. All input therefore contains at least two lines of the following form:
STATES state1 state2
QUANTA l1 l2
STATES state1 state2
The filenames of two TAPE21 files resulting from a numerical or analytical frequency calculation. The calculations must have been performed on the same molecule, i.e. the type, mass and order of occurence of all the atoms (or fragments) has to be the same in both files.
(optional) MODES first last
The first and last mode to be taken into account in the calculation. If this option is omitted, all modes are taken into account. This option can be used to effectively specify and energy range for the Franck-Condonf factors. When using this options, always check if the results (electron-phonon couplings, ground state to ground overlap integral, average sum of Franck-Condon factors, etc.) do not change too much.
(optional) LAMBDA lambda
The minimum value of the electron-phonon coupling for a mode to be taken into account in the calculation. The default value is zero. Together with the MODES option, this provides a way to significantly reduce the total number of Franck-Condon factors. As with the MODES option, always check if the results do not change too much.
QUANTA l1 l2
The maximum number of vibrational quanta to be taken into account for both states. Franck-Condon factors will be calculated for every permutation of up to and including l1/l2 quanta over the vibrational modes.
(optional) TRANSLATE
Move the center of mass of both geometries to the origin.
(optional) ROTATE
Rotate the geometries to maximize the overlap of the nuclear coordinates.
Only a few keys from the TAPE21 file are used for the calculation of the Franck-Condon factors. Disk space usage can be significantly reduced by extracting just these keys from the TAPE21 file before further analysis. The following shell script will extract the keys from the KF file specified by the first argument and store them in a new KF file specified by the second argument using the cpkf utility:
#!/bin/sh
cpkf $1 $2 "Geometry%nr of atoms" "Geometry%xyz" "Geometry%nr of atomtypes" \
"Geometry%fragment and atomtype index" "Geometry%atomtype" "Geometry%mass" \
"Freq%Frequencies" "Freq%Normalmodes"
