xenial (1) detcas.1.gz

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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)