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PROGRAM:

NAME


detcas - Determinant Configuration Interaction / Complete Active
Space Self-Consistent-Field Program

DESCRIPTION


The program detcas performs a complete-active-space self-consistent-field (CASSCF)
optimization of molecular orbitals via a two-step procedure in conjunction with the
determinant configuration interaction program DETCI. The program is fairly simple and
currently uses a Newton-Raphson approach to update the orbitals, employing a simple
approximate orbital Hessian. Convergence is accelerated using Pulay's direct inversion of
the iterative subspace (DIIS) procedure. The code has been written to allow more general
wavefunctions that do not necessarily feature a full CI treatment of the active space. In
particular, any restricted active space (RAS) CI wavefunction supported by DETCI can be
used, allowing MCSCF wavefunctions of the RASSCF type.

REFERENCES


Approximate Orbital Hessian:

1. G. Chaban, M. W. Schmidt, and M. S. Gordon, Theor. Chim. Acta 97, 88-95 (1997).

Restricted Active Space CI:

1. Determinant Based Configuration Interaction Algorithms for Complete and Restricted
Configuration Interaction Spaces, J. Olsen, B. O. Roos, P. Jorgensen, and H. J. Aa.
Jensen, J. Chem. Phys. 89, 2185 (1988).

Restricted Active Space SCF:

1. P.-A. Malmqvist, A. Rendell, and B. O. Roos, J. Phys. Chem. 94, 5477 (1990).

DETCI Program:

1. C. D. Sherrill, Computational Algorithms for Large-Scale Full and Multi-Reference
Configuration Interaction Wavefunctions, PhD thesis, University of Georgia, Athens,
GA, 1996.

2. C. D. Sherrill and H. F. Schaefer, The Configuration Interaction Method: Advances
in Highly Correlated Approaches, Adv. Quantum Chem. 34, 143-269 (1999).

FILES REQUIRED


input.dat - Input file
file78 - MO one-electron integrals (fzc operator)
file72 - MO two-electron integrals
file73 - MO one-particle density matrix
file74 - MO two-particle density matrix
file75 - MO Lagrangian

FILES UPDATED


output.dat - Output file
file14.dat - Record of energies and orbital gradients

INPUT FORMAT


The following command-line arguments are available:

-quiet This gives the same result as PRINT=0.

-o fname
Gives the filename for the output file. Defaults to output.dat.

Additional input for this program is read from the file input.dat. The more commonly used
keywords are:

WFN = string
The supported wave function types are CASSCF and RASSCF.

CONVERGENCE = integer
Convergence desired on the orbital gradient. Convergence is achieved when the RMS
of the error in the orbital gradient is less than 10**(-n). The default is 4 for
energy calculations and 7 for gradients.

DOCC = integer_array
This vector gives the number of doubly occupied orbitals in each irrep. There is
no default.

SOCC = integer_array
This vector gives the number of singly occupied orbitals in each irrep. There is
no default.

ENERGY_CONVERGENCE = integer
Convergence desired on the total MCSCF energy. The default is 7.

FROZEN_DOCC = integer_array
The number of lowest energy doubly occupied orbitals in each irreducible
representation which will literally be frozen (not updated in the MCSCF). The
Cotton ordering of the irredicible representations is used. The default is the
zero vector.

FROZEN_UOCC = integer_vector
The number of highest energy unoccupied orbitals in each irreducible representation
which will literally be frozen (not updated in the MCSCF). The default is the zero
vector.

RESTRICTED_DOCC = integer_array
The number of lowest energy doubly occupied orbitals in each irreducible
representation which will be optimized but kept doubly occupied in the MCSCF.
These orbitals come after the FROZEN_DOCC orbitals. The default is the zero
vector.

RESTRICTED_UOCC = integer_array
The number of highest energy unoccupied orbitals in each irreducible representation
which will be optimized but kept unoccupied in the MCSCF. These orbitals come
before the FROZEN_UOCC orbitals. The default is the zero vector.

NCASITER = integer
Maximum number of iterations to optimize the orbitals. This option should be
specified in the DEFAULT section of input, because it needs to be visible to the
control program PSI. Defaults to 1.

PRINT = integer
This option determines the verbosity of the output. A value of 1 or 2 specifies
minimal printing, a value of 3 specifies verbose printing. Values of 4 or 5 are
used for debugging. Do not use level 5 unless the test case is very small (e.g.
STO H2O CISD).

The less commonly used keywords are:

DIIS_FREQ = integer
The DIIS extrapolation procedure will be attempted every n iterations. The default
is 1.

DIIS_MAX_VECS = integer
The maximum number of subspace vectors for the DIIS procedure. After this number
of vectors are reached, older vectors will be dropped from the subspace as
necessary. The default is 8.

DIIS_MIN_VECS = integer
The minimum number of subspace vectors before a DIIS interpolation can be
performed. The default is 2. It doesn't make sense to have values less than 2.

DIIS_START = integer
The iteration number when Pulay's Direct Inversion of the Iterative Subspace (DIIS)
procedure for acceleration of convergence should be turned on. The default is 3.
Prior to this iteration, vectors are not added to the DIIS subspace. The first
DIIS step will not be taken until DIIS_MIN_VECS vectors are in the DIIS subspace.

LAG_FILE = integer
File (unit number) for reading the lagrangian matrix. The default value is
currently 75.

OPDM_FILE = integer
File (unit number) for reading the one-particle density matrix. The default value
is currently 73.

SCALE_GRAD = boolean
Tells whether to scale the orbital gradient by the approximate (diagonal) orbital
Hessian. The default is TRUE.

SCALE_STEP = real
Scale factor for the orbital rotation step. Default is 1.0.

TPDM_FILE = integer
File (unit number) for reading the two-particle density matrix. The default value
is currently 74.

LEVEL_SHIFT = boolean
Tells whether to allow for level shifting of the hessian matrix. This can be used
to ensure that the hessian is positive definite for the beginning iterations. If
the hessian is not positive definite near convergence, then this may be a sign of
numerical instabilities in the MCSCF. The default is TRUE.

SHIFT = real
Tells how much the diagonal elements of the hessian should be shifted for level
shifting. Default is 0.01.

DETERM_MIN = real
Minimum allowed valued for the determinant of the hessian matrix if level shifting
is on. This is not used if LEVEL_SHIFT=FALSE. Default is 0.00001.

STEP_MAX = real
This is the maximum allowed single orbital rotation. Default is 0.30.

FORCE_STEP = boolean
This allows the user to overide the calculated step and to force a step in a
particular direction. This can be useful if trying to force the calculation away
from a saddle point. The default is FALSE.

FORCE_PAIR = integer
This is the index for the independent pair which is to be rotated if
FORCE_STEP=TRUE. This is ignored otherwise. There is no default.

FORCE_VALUE = real
This is the orbital rotation value for rotating the orbitals specified by
FORCE_PAIR. This is only used if FORCE_STEP is set to TRUE. The default value is
0.0.

CHECK_HESSIAN = boolean
Calculate the eigenvalues of the orbital hessian. This is good for checking for
saddle-point solutions. Should be used without level shifting. The default is
FALSE.

EIGEN_VECTORS = boolean
Do you want to calculate the eigenvectors of the orbital hessian as well. This is
ignored if CHECK_HESSIAN=FALSE. Default is FALSE.

8 May, 1998 detcas(1)

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