keyword selects the Symmetry Adapted Cluster/Configuration Interaction (SAC-CI)
methods of Nakatsuji and coworkers [121,122,123,124,125,126,127,128,129,130,131,132,133,134,135].
For detailed information on this method, consult the SAC-CI documentation available
at the following web site: www.sbchem.kyoto-u.ac.jp/nakatsuji-lab.
jobs must specify a reference state for the subsequent excited states calculations.
For closed shell systems, the default RHF wavefunction used by SAC-CI is appropriate.
For open shell ground states, you must either select an ROHF ground state wavefunction
by including ROHF in the route section in addition to SAC-CI, or
you must specify a closed shell state for the ground state calculation using the
AddElectron or SubElectron option. See the examples for more information.
that singlet states are to be calculated. The parenthesized list of suboptions
specifies the desired states and other calculation parameters. Other spin state
selection options are CationDoublet (Doublet is a synonym), AnionDoublet,
Triplet, Quartet, Quintet, Sextet and Septet.
More than one spin state may be specified.
SPIN STATE SUBOPTIONS
Sets the number of states of the specified type to be calculated for the
various irreducible representations of the molecule's point group. Up to eight
values may be specified, depending on the molecular symmetry (e.g., 8 for D2h,
4 for C2v, and so on). The shorthand form NState=N specifies
a value of N for each irreducible representation. Degeneracies are handled
by assuming the closest linear symmetry (e.g., D2 for Td).
density matrices and perform Mulliken population analysis for all computed SAC-CI
states of spin SpinState. See the examples for more information.
Calculate spin density matrices for all computed SAC-CI states of spin
SpinState. Implies the FullActive option as well.
By default, the transition density and oscillator strength are calculated
between the SAC ground state and the SAC-CI singlet excited states when SpinState
is Singlet, and between the lowest SAC-CI states and SAC-CI excited
states for other spin states. NoTransitionDensity disables these calculations
for the corresponding spin state.
OTHER COMMONLY-USED OPTIONS
Specifies the target
state for a geometry optimization or a gradient calculation, or for use with the
Density keyword. S is the keyword indicating
its spin multiplicity (i.e., Singlet, Doublet, etc.), m is
the irreducible representation number of its point group, and n is the
solution number in the desired spin state (determined by a previous energy calculation).
Add one electron to the open shell reference SCF
configuration. This is the default for such systems for CationDoublet,
Doublet, Quartet and Sextet.
Subtract one electron from the open shell reference SCF configuration. This is
the default for such systems for AnionDoublet.
Symmetry=m, Root=n)Specifies the initial
state for for calculating transition density matrices. S is the keyword
indicating its spin multiplicity (i.e., Singlet, Doublet, etc.),
m is the irreducible representation number of its point group, and n
is the solution number in the desired spin state (as for TargetState above).
Calculate multipole moments through hexadecapole,
all Nth moment to the 4th moment, all electrostatic properties and the
diamagnetic terms (shielding and susceptibility). This option applies to all spin
states which specify the Density suboption.
Don't calculate any molecular properties.
the calculation after the CIS initial guess has been calculated. You can use this
option to determine the state number of a particular state in which you are interested
(e.g., for TargetState). See the examples for an alternative method.
Performs only the calculation for the reference state and does not compute any
ADDITIONAL OPTIONS FOR EXPERT
ADDITIONAL SPIN STATE SUBOPTIONS
Set the maximum excitation level to N.
Solve the SAC-CI equations for non-symmetric matrices. Variational
proceeds by diagonalizing symmetrized matrices, and it is the default. Note that
this option only applies to the excited state portion of the calculation (the
ground state calculation always uses a nonvariational procedure).
Force use of the in-core algorithm.
Force the use of an iterative algorithm. Item specifies the initial
guess type: SInitial for CIS and SDInitial for CISD.
The frozen-core options for
defining inner-shells to be excluded from the correlation calculation are valid
with this keyword. In general, the size of the active space greatly affects the
accuracy of SAC-CI calculations. For this reason, using a full orbital window
is recommended. Full is the default for geometry optimizations and gradient
LMO=type Use the specified type of localized
MO as reference orbitals. The available types are PM (Pipek-Mezey) and
Requests the use
of N macroiterations within an optimization step. The default value of
N is 0.
For solution of the SAC equations
using the in-core algorithm.
Set the maximum
number of diagonalization iterations.
maximum number of iterations for solving the SAC equations.
Set the diagonalization energy convergence criteria to 10-M.
Set the energy convergence criteria to 10-M when solving the SAC equations.
Perform the calculation
using singles and doubles linked excitation operators. This is the default.
Perform the calculation including linked excitation operators through sextuples.
Set the threshholds for selection of the double excitation operators to the lowest
recommended level. LevelThree is the most accurate level, and it is the
default. LevelTwo is intermediate in accuracy between the other two levels.
By default, perturbation selection is performed so that degeneracies are
retained. This option suppresses this test, resulting in reduced computational
requirements. Use of this option is not recommended for production use.
Disables perturbation selection threshholds for linked operators (i.e.,
all operators are included).
perturbation selection threshholds for unlinked operators (i.e., all operators
Include all types of unlinked
terms. Forces the use of the in-core algorithm.
In order to include all
terms, all three of these preceding options are required, currently at a considerable
Ignore R2S2 unlinked integrals.
This option results in a tradeoff between decreased accuracy and computational
Generate quadruple and higher-order linked
operators in the General-R scheme via the exponential generation algorithm.
This is the default for single point energy calculations. The highest order excitation
level is specified via the MaxR option (up to a maximum of 6). Perturbation
selection threshholds are set via the LevelOne, LevelTwo and LevelThree
Generate all higher-order linked operators
in the General-R scheme up to MaxR=4 and then perform perturbation
selection as above. This is the default for gradient calculations and geometry
GROUP SUM OPERATION OPTIONS
These options are used
to ensure consistency between all points in multipoint calculation types like
potential energy surface scans. The Scan calculation must be performed
three times: at the first point with BeforeGSUM, then at some or all subsequent
points with CalcGSUM and then finally at all points with AfterGSUM.
The actual results are provided by the final calculation. This procedure is only
valid for singlet, triplet, ionized and electron-attached states, and it is not
compatible with the General-R option.
a series of linked calculations. Use this option in a calculation at the first
Collect data and determine the threshholds and
operator selections at specified points in order to form a consistent set which
can then be used at every point.
Perform SAC-CI calculations
at each point using the GSUM data collected previously with the CalcGSUM
MEMORY USE OPTIONS
These options can be used to increase
the program default settings after a failed job has indicated that a resource
shortfall was the problem.
Set the maximum number
of R2 operators after perturbation selection to N. The default is 100,000.
Set the maximum number of operators in the General-R method to N.
The default is 5,000.
and optimizations and numerical frequencies.
Geometry optimizations default
to using a full window. Specifying a different frozen core option for an optimization
will result in numerical gradient calculations and correspondingly poorer performance.
you want to locate the lowest two singlet excited states, you could use a route
like the following:
# SAC-CI=(Full,Singlet=(NState=8))/6-31G(d) NoSymm ...
search for 8 singlet states, ignoring symmetry. The two lowest excited states
will probably be among those found by the calculation.
could use the following route:
# SAC-CI=(Full,Singlet=(NState=4))/6-31G(d) ...
This calculation will locate the lowest four singlet excited states for
each irreducible representation.
To specify the desired number of singlet excited states for each irreducible
representation for a molecule with C2v symmetry, use a route
like this one:
# SAC-CI=(Full, Singlet=(2,2,1,2))/6-31G(d) ...
States with an Inexpensive Initial Calculation. You can use a preliminary,
lower-accuracy calculation in order to locate a desired excited state at reduced
computational cost. For example, the following route will locate 4 singlet excited
states of each symmetry type:
# SAC-CI=(Full,Singlet=(NState=4),LevelOne)/6-31G(d) ...
could be followed by a normal (LevelThree) calculation for the state(s)
of interest. For example:
# SAC-CI=(Full,Singlet=(1,0,1,0))/6-31G(d) ...
on Open Shell Systems. To predict excited states for vinyl radical, a neutral
doublet radical, you could use a route like the following:
# ROHF/6-31G(d) SAC-CI=(Full,Doublet=(NState=3),Quartet=(NState=3)) ...
This specifies the use of an ROHF wavefunction for the ground state,
and it computes three doublet and three quartet excited states for each irreducible
representation. You could use a similar approach for the triplet ground state
Geometry Optimizations. To optimize a specific excited
state, use the TargetState option:
# Opt SAC-CI=(Singlet=(Nstate=4),
Computing Densities and Molecular Properties. To compute the
unrelaxed density and population analysis for all predicted excited states, use
a route like this one:
# SAC-CI=(Full,Singlet=(...,Density),Triplet=(...,Density))/6-31G(d) ...
If you wanted to compute the unrelaxed density and population analysis
only for the triplet states, then you would omit the Density suboption
to the Singlet option.
compute the relaxed density and population analysis for only one specified state,
use a route like the following:
# SAC-CI=(Full,Singlet=(NState=4),TargetState=(...)) Density=Current ...
Note that this job will be much more computationally expensive than the
previous one as it requires a full gradient calculation.
Output. SAC-CI calculations produce a table like the following for each requested
spin state (this example is for singlet states):
Transition dipole moment of singlet state from SAC ground state
Symmetry Sol Excitation Transition dipole moment (au) Osc.
energy (eV) X Y Z strength
A1 0 0.0 Excitations are from this state.
A1 1 8.7019 0.0000 0.0000 0.4645 0.0460
A1 2 18.9280 0.0000 0.0000 -0.4502 0.0940
A1 3 18.0422 0.0000 0.0000 -0.8904 0.3505
A1 4 18.5153 0.0000 0.0000 0.0077 0.0000
A2 1 7.1159 0.0000 0.0000 0.0000 0.0000
A2 2 18.2740 0.0000 0.0000 0.0000 0.0000
B1 1 1.0334 -0.2989 0.0000 0.0000 0.0023
B1 2 18.7395 -0.6670 0.0000 0.0000 0.2042
B1 3 22.1915 -0.1500 0.0000 0.0000 0.0122
B1 4 15.8155 0.8252 0.0000 0.0000 0.2639
B2 1 11.0581 0.0000 0.7853 0.0000 0.1671
B2 2 15.6587 0.0000 1.5055 0.0000 0.8696
B2 3 24.6714 0.0000 -0.7764 0.0000 0.3644
B2 4 23.5135 0.0000 -0.1099 0.0000 0.0070
Note that the various excited states are grouped by symmetry type—and
not in order of increasing energy—in the output.