# SAC-CIThe
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*. SAC-CI
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. ### SPIN
STATE OPTION**Singlet=(***suboptions***)**
Specifies
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*SpinState***=(NState=(***i*_{1},*i*_{2},...**))**
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 D_{2h},
4 for C_{2v}, 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., D_{2} for T_{d}).
*SpinState***=**(**Density**)
Calculate unrelaxed
density matrices and perform Mulliken population analysis for all computed SAC-CI
states of spin *SpinState*. See the examples for more information.
*SpinState***=**(**SpinDensity**)
Calculate spin density matrices for all computed SAC-CI states of spin
*SpinState*. Implies the **FullActive **option as well.
*SpinState***=**(**NoTransitionDensity**)
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**TargetState=(SpinState=***s***,
Symmetry=***m***, Root=***n***)**
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).
**AddElectron** Add one electron to the open shell reference SCF
configuration. This is the default for such systems for **CationDoublet**,
**Doublet**, **Quartet** and **Sextet**.
**SubElectron**
Subtract one electron from the open shell reference SCF configuration. This is
the default for such systems for **AnionDoublet**.
**TransitionFrom=(SpinState=***s***,
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).
**AllProperties** Calculate multipole moments through hexadecapole,
all *N*th 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.
**NoProperty**
Don't calculate any molecular properties.
**SelectCISOnly** Terminate
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.
**SACOnly**
Performs only the calculation for the reference state and does not compute any
excited states.
### ADDITIONAL OPTIONS FOR EXPERT
USERS### ADDITIONAL SPIN STATE SUBOPTIONS*SpinState***=(MaxR=***N***)**
Set the maximum excitation level to *N*.
*SpinState***=**(**NonVariational**)
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).
*SpinState***=**(**InCoreDiag**)
Force use of the in-core algorithm.
*SpinState***=**(**Iterative=***item*) Force the use of an iterative algorithm. *Item* specifies the initial
guess type: **SInitial** for CIS and **SDInitial** for CISD.
### PROCEDURAL
OPTIONS**FC** 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
calculations.
**LMO=***type* Use the specified type of localized
MO as reference orbitals. The available types are **PM** (Pipek-Mezey) and
**Boys**.
**MacroIteration=***N* Requests the use
of *N *macroiterations within an optimization step. The default value of
*N* is 0.
**InCoreSAC** For solution of the SAC equations
using the in-core algorithm.
**MaxItDiag=***N* Set the maximum
number of diagonalization iterations.
**MaxItSAC=***N* Set the
maximum number of iterations for solving the SAC equations.
**DConvDiag=***M*
Set the diagonalization energy convergence criteria to 10^{-M}.
**DConvSAC=***M*
Set the energy convergence criteria to 10^{-M} when solving the SAC equations.
### ACCURACY
LEVEL OPTIONS
_{}**SD-R** Perform the calculation
using singles and doubles linked excitation operators. This is the default. **General-R**
Perform the calculation including linked excitation operators through sextuples.
**LevelOne**
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.
**WithoutDegeneracy** 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.
**NoLinkedSelection** Disables perturbation selection threshholds for linked operators (i.e.,
all operators are included).
**NoUnlinkedSelection** Disables
perturbation selection threshholds for unlinked operators (i.e., all operators
are included).
**FullUnlinked** 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
performance penalty. **WithoutR2S2** Ignore R2S2 unlinked integrals.
This option results in a tradeoff between decreased accuracy and computational
requirements.
**EgOp** 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**
options.
**FullRGeneration** 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
optimizations.
### GROUP SUM OPERATION OPTIONSThese 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. **BeforeGSUM** Initialize
a series of linked calculations. Use this option in a calculation at the first
point.
**CalcGSUM** 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.
**AfterGSUM** Perform SAC-CI calculations
at each point using the GSUM data collected previously with the **CalcGSUM**
option.
### MEMORY USE OPTIONSThese options can be used to increase
the program default settings after a failed job has indicated that a resource
shortfall was the problem. **MaxR2Op=***N* Set the maximum number
of R2 operators after perturbation selection to *N*. The default is 100,000.
**MaxEgOp=***N*
Set the maximum number of operators in the **General-R** method to *N*.
The default is 5,000.
Analytic energies
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. **Density**
If
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 *...*
This will
search for 8 singlet states, ignoring symmetry. The two lowest excited states
will probably be among those found by the calculation. Alternatively, you
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 C_{2v} symmetry, use a route
like this one:
# SAC-CI=(Full, Singlet=(2,2,1,2))/6-31G(d) *... *
* ***Locating
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) *...*
This job
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) *...*
**Calculations
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
of methylene. **Geometry Optimizations**. To optimize a specific excited
state, use the **TargetState** option:
# Opt SAC-CI=(Singlet=(Nstate=4),
TargetState=(SpinState=Singlet,Symmetry=1,Root=2))/6-31G(d) *...*
**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.
* *To
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.
**SAC-CI
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. |