Provided by: psi3_3.4.0-6_amd64 
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)