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 $cis group.
It is intended for geometry optimization of the excited states in the
case of root flipping.
Note that oscillator strengths printed in the CIS summary table are calculated
using transition dipoles length form only.
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$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.
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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:
J.B.Foresman, M.Head-Gordon, J.A.Pople, M.J.Frisch J.Phys.Chem. 96, 135-149(1992)
R.M.Shroll, W.D.Edwards Int.J.Quantum Chem. 63, 1037-1049(1997)
S.P.Webb Theoret.Chem.Acc. 116, 355-372(2006)
Last updated: March 18, 2009