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.

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.