PC GAMESS/Firefly CIS MODULE DOCUMENTATION.

$CIS group                      required when CITYP=CIS

   The CIS method (singly excited CI) is the simplest way
to treat excited states.  By Brillouin's Theorem, a single
determinant reference such as RHF will have zero matrix
elements with singly substituted determinants.  The ground
state reference therefore has no mixing with the excited
states treated with singles only.  Reading the references
given in Section 4 of this manual will show the CIS method
can be thought of as a non-correlated method, rigorously
so for the ground state, and effectively so for the various
excited states.  Some issues making CIS rather less than a
black box method are:
    a) any states characterized by important doubles are
       simply missing from the calculation.
    b) excited states commonly possess Rydberg (diffuse)
       character, so the AO basis used must allow this.
    c) excited states often have different point group
       symmetry than the ground state, so the starting
       geometries for these states must reflect their
       actual symmetry.
    d) excited state surfaces frequently cross, and thus
       root flipping may very well occur.

   The CIS code in the PC GAMESS/Firefly is based on heavily
modified sources of the original GAMESS (US) AO-basis CIS code
written by Dr. Simon P. Webb (Ref. 3 below).

The implementation allows the use of only RHF references,
but can pick up both singlet and triplet excited states.
Nuclear gradients are available, as are properties.

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.

HAMTYP =   Type of CI Hamiltonian to use.
       =   SAPS spin-adapted antisymmetrized product of
                the desired MULT will be used (default)
       =   DETS determinant based, so both singlets and
                triplets will be obtained. Note that this
                option will disable use of FASTINTS/GENCON
                code during direct CIS runs.

MULT   =   Multiplicity (1 or 3) of the singly excited
           SAPS (the reference is necessarily single RHF).
           Only relevant for SAPS based run.

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).

DGAPRX =   Flag to control whether approximate diagonal
           elements of the CIS Hamiltonian (based only on
           the orbital energies) are used in the Davidson
           algorithm.  Note, this only affects the rate of
           convergence, not the resulting final energies.
           If set .FALSE., the exact diagonal elements are
           determined and used.  Default=.TRUE.

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.
           Default=50.

DAVCVG =   Convergence criterion for Davidson eigenvectors.
           Eigenvector accuracy is proportional to DAVCVG,
           while the energy accuracy is proportional to its
           square.  The default is 1.0E-05.

CISPRP =   Flag to request the determination of CIS level
           properties, using the relaxed density.  Relevant
           to RUNTYP=ENERGY jobs, although the default is
           .FALSE. because additional CPHF calculation will
           be required.  Properties are computed as a normal
           byproduct of runs involving the CIS gradient.

CHFSLV =   Chooses type of CPHF solver to use.
       =   CONJG selects an ordinary preconditioned conjugate
                 gradient solver.  This is the default.
       =   DIIS  selects a diis-like iterative solver.

RDCISV =   Flag to read CIS vectors from a $CISVEC group
           in the input file.  Default is .FALSE.

MNMEDG =   Flag to force the use of the minimal amount of
           memory in construction of the CIS Hamiltonian
           diagonal elements.  This is only relevant when
           DGAPRX=.FALSE., and is meant for debug purposes.
           The 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.



          The additional PC GAMESS/Firefly specific keywords are:

CPTOL - convergence criterion for CPHF equations, default is 1.0d-5 for
GAMESS (US) compatibility.

THRDII - threshold to turn on DIIS if it was selected to solve CPHF.
Default is 0.05

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.

ONEDIM = .true./.false. Default is true for abelian groups, false otherwise.
Option to select fast algorithm for excited state properties/gradients for
systems with symmetry. Any state transforming by any pure one-dimension
representation on the point group can be handled by this manner.
It is safe to always turn this option on as the check is performed and this
option disables itself if the symmetry is not appropriate.

PRTTOL - threshold for CIS determinants/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 in the GAMESS (US).

ICUTCP - the effective value of ICUT to be used by CONJG CPHF solver 
while solving CPHF equations in direct SCF mode. The main purpose of 
this keyword is to avoid numerical instability problems causing conjugate
gradient solver to diverge upon reaching near-convergence. E.g., one may 
set ICUT to 9 or 10 while tighten ICUTCP to be 10 or 11. The default is the 
value of ICUF of $CONTRL group.

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

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

==========================================================
$CISVEC group     required if RDCISV in $CIS is chosen

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


Below is the sample input file.


 $CONTRL SCFTYP=RHF CITYP=CIS $END
 $SYSTEM TIMLIM=3000 MEMORY=3000000 $END
 $BASIS  GBASIS=n31 ngauss=6 NDFUNC=1 $END
 $CIS NSTATE=3 ISTSYM=0 ISTATE=1 $END
 $DATA
H2O
CNV 2

 O           8.0   0.0000000000   0.0000000000   0.7205815395
 H           1.0   0.0000000000   0.7565140024   0.1397092302
 $END

Selected CIS references:

1. J.B.Foresman, M.Head-Gordon, J.A.Pople, M.J.Frisch J.Phys.Chem. 96, 135-149(1992)

2. R.M.Shroll, W.D.Edwards Int.J.Quantum Chem. 63, 1037-1049(1997)

3. S.P.Webb Theoret.Chem.Acc. 116, 355-372(2006)

See also:

• PC GAMESS/Firefly input preprocessing sample
• 64-bit processing support
• Fast Matrix Diagonalization and Inversion
• Spherical Basis Functions
• Fast Two-electron Integral Code
• Additional comments on Two-electron Integral code selection
• Quantum Fast Multipole Method
• Time-dependent Hartree-Fock
• Time-dependent DFT
• CI and Multi-Configuration SCF
• Multi-Configuration Quasi-Degenerate Perturbation Theory
• Extended Multi-Configuration Quasi-Degenerate Perturbation Theory (XMCQDPT)
• Potential Energy Surface scans
• PC GAMESS/Firefly' NBO code
• Cube Files
• Multicore, SMP and HTT support
• P2P Parallel Mode Communication Interface, Dynamic Load Balancing, and large-scale MP2 Energy code
• Parallel Linux Instructions: list of supported MPI implementations
• Parallel Windows Instructions: list of supported MPI implementations/bindings

Last updated: March 18, 2009