detcas(1)

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. This would only require changes to the subroutine which calculates the approximate orbital Hessian.

REFERENCES

Approximate Orbital Hessian:

1.  G. Chaban, M. W. Schmidt, and M. S. Gordon, Theor. Chim. Acta, xxx.

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., in press.

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 following keywords are valid:

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.

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.

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.

FCI = boolean
    If this flag is set to TRUE, then rotations of orbitals within the active space are not considered. Currently, the program will not work unless this is TRUE. The default is TRUE.

FROZEN_DOCC = integer_array
    The number of lowest energy doubly occupied orbitals in each irreducible representation from which there will be no excitations. The Cotton ordering of the irredicible representations is used. The default is the zero vector. These orbitals are not really frozen in an MCSCF procedure...they are optimized.

FROZEN_UOCC = integer_vector
    The number of highest energy unoccupied orbitals in each irreducible representation into which there will be no excitations. The default is the zero vector. These orbitals are not really frozen in an MCSCF procedure...they are optimized.

FREEZE_CORE =  boolean
    This option determines whether the frozen core orbitals are to be frozen in their SCF form (TRUE) or optimized by the MCSCF (FALSE). Currently, only FALSE is supported. The default is FALSE.

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

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.

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

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).

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.