$TDDFT group                       required when CITYP=TDDFT
(note that CITYP=TDDFT requires DFTTYP to be set in $CONTRL)

   Current implementation allows the use of only R-DFT references,
but can pick up both singlet and triplet excited states.
Nuclear gradients are programmed with Firefly version 8.1 onwards. 
Properties are available using "unrelaxed" density and for "relaxed" 
density (with Firefly version 8.1 onwards). Due to efficiency considerations, 
TDDFT is programmed for SAPS (spin-adapted antisymmetrized product) 
basis only, so you cannot get both singlet and triplet states at once.

NCORE = n  Omits the first n occupied alpha and beta orbitals from
           the calculation.  The default for n is the number
           of chemical core orbitals.

NSTATE =   Number of states to be found (excluding the
           ground state).

ISTATE =   State for which properties and/or gradient will
           be calculated.  Only one state can be chosen.

MULT   =   Multiplicity (1 or 3) of the singly excited
           SAPS (the reference is necessarily single R-DFT).

DIAGZN =   Hamiltonian diagonalization method.
       =   DAVID use Davidson diagonalization.  (default)
       =   FULL  construct the full matrix in memory and
                 diagonalize, thus determining all states
                 (not recommended except for small cases).

NGSVEC =   Dimension of the Hamiltonian submatrix that is
           diagonalized to form the initial CI vectors.
           The default is the greater of NSTATE*2 and 10.

MXVEC  =   Maximum number of expansion basis vectors in the
           iterative subspace during Davidson iterations,
           before the expansion basis is truncated.  The
           default is the larger of 8*NSTATE and NGSVEC.

NDAVIT =   Maximum number of Davidson iterations.

DAVCVG =   Convergence criterion for Davidson eigenvectors.
           Eigenvector accuracy is proportional to DAVCVG,
           while the energy accuracy is proportional to its
           square.  The default is 3.0E-05.

RDTDVC =   Flag to read TDDFT vectors from a $TDVEC group
           in the input file.  Default is .FALSE.

MNMEOP =   Flag to force the use of the minimal amount of
           memory during the Davidson iterations. This is
           for debug purposes. The default is .FALSE.

MAXGC - maximum allowed number of trial vectors to be routed through GENCON
engine, default is 1. If the number of trial vectors is greater than MAXGC,
only FASTINTS will be used. The reason is that for moderately contracted GC
basis sets like cc-pVXZ, gencon is faster than fastints only for relatively
small number of trial vectors (this is by gencon design). On the other hand,
for ANO-like basis sets, it is always better to set MAXGC to be equal the
number of initial guess vectors, as fastints will be much slower.

PRTTOL - threshold for TDDFT csf printout and also for states symmetry
determination. Default is 0.05.

ISTSYM - symmetry of states of interest. Default is zero, i.e., does not use
any symmetry during calculations. Setting this to the desired index of irrep
(according to PC GAMESS/Firefly numbering) will solve only for the states of
the desired symmetry and exploiting full (including non-abelian) symmetry of
molecule, thus significantly reducing computation time.

ALTER - flag to modify internal logic of Davidson diagonalization code to
use dynamic number of trial vectors. Default is .true. Setting it to .false.
will slow-down calculations by forcing DAVIDSON diagonalization code to work
exactly as CIS code in the GAMESS (US).

TDA  - flag to request Tamm-Dancoff approximation to TDDFT (TDDFT/TDA),
which is programmed for both pure and hybrid functionals. Default is .false.

The state-tracking feature of the PC GAMESS/Firefly' TDDFT code can be
activated by selecting negative value of istate in the $TDDFT group.
It is intended for geometry optimization of the excited states in the
case of root flipping.

Note that oscillator strengths printed in the TDDFT summary table are calculated
using transition dipoles length form only.

$TDVEC group     required if RDTDVC in $TDDFT is chosen

This is formatted data generated by a previous TDDFT run, to
be read back in as starting vectors.

Below is the sample input file:

 $BASIS  GBASIS=n31 ngauss=6 NDFUNC=1 $END

 O           8.0   0.0000000000   0.0000000000   0.7205815395
 H           1.0   0.0000000000   0.7565140024   0.1397092302

The example of TDDFT/TDA calculations:

 $BASIS  GBASIS=n31 ngauss=6 NDFUNC=1 $END

 O           8.0   0.0000000000   0.0000000000   0.7205815395
 H           1.0   0.0000000000   0.7565140024   0.1397092302

See also:

Last updated: August 24, 2013