`WF`=*type*- Defines the type of the wavefunction.
`WF=VSCF`specifies state-specific`VSCF`wavefunctions for both levels, while`WF=VCI`denotes state-specific`VCI`wavefunctions. Alternatively, one may use`WF=VSCFG`for ground-state based VSCF wavefunctions and`WF=VCIG`for ground-state based VCI wavefunctions. The default is`WF=VCI`. `THRPRINT`=*value*- This keyword defines the smallest value of a Franck-Condon factor to be printed in the output. The default is set to 1.0d-99, i.e. this
threshold usually is inactive.
`THRFCFSPEC`=*value*- This threshold controls, if a Franck-Condon factor will be considered within the plotting of the spectrum. See the
`PUT`command and the`IRSPEC`style. The default is 1.0d-6. `THRFCF`=*value*- The sum of all Franck-Condon factors is 1.0d0 by definition. However, this value is hard to reach by sum over states approaches. Therefore,
it can be lowered by this keyword.
`THRDELTA`=*value*- The -criterion is a threshold, which allows for the prescreening of overlap integrals within the evaluation of the
Franck-Condon factors prior to their evaluation. The default is set to 1.0d-8.
`THRSKIPBAS`=*value*- Basis functions in the outer regions of the potentials may be skipped within the calculation of Franck-Condon factors. In particular within
the approach of Doktorov, the CPU time depends strongly on the number of basis functions. This keyword allows to skip such basis
functions and is given as the overlap integral of the modal. The default is 0.999999d0.
`THRSEL`=*value*- This threshold controls, if a Franck-Condon factor shall be selected and thus be considered in all subsequent calculations or not.
The default is 1.0d-5.
`THRVCIMIN`=*value*- Within the calculation of Franck-Condon factors based on VCI wavefunctions, the leading VCI coefficient should be largest in order to
correspond to the state of interest. The default is set to 0.01d0, which of course means that this keyword essentially is inactive.
`THRSUMSEL`=*value*- This threshold controls the sum of the selected Franck-Condon factors, which must formally be 1.0d0. The default is set to 0.999999d0.
`MAXSEL`=*n*`MAXSEL=n`determines the maximum number of Franck-Condon factors to be selected. By default*n*is set to 100.`SEL`=*n*- This option switches the selection of Franck-Condon factors based on VSCF calculation on (
`SEL=1`) or off (`SEL=0`, default). `DUSCH`=*n*- This keyword controls the Duschinsky transformation.
`DUSCH=0`entirely neglects the Duschinsky transformation - including the shift-vector.`DUSCH=1`switches the Duschinsky transformation on and the algorithm of Doktorov will be used. Note that this option is only limited to 3-atomic systems.`DUSCH=3`neglects the Duschinsky rotation, but includes the shift-vector. This is the default option as the Duschinsky rotation can be passed to the`PESTRANS`program, which is much more efficient. `ECKART`=*n*`ECKART=1`(default) determines the Eckart transformation matrix as described in the literature.`ECKART=0`approximates the Eckart transformation matrix by a unit matrix, which is meaningless unless for debugging purposes or for some very special tests.

Some of the keywords as described for the `VCI` program are
also valid for the `FCON` program, i.e. `CITYPE, LEVEX, CIMAX, DIPOLE,
NDIM, NBAS, NGRID, BASIS` and `INFO`.