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NAME

       cscf - solves the Hartree-Fock equations

DESCRIPTION

       The program cscf carries out the iterative procedure to solve the Hartree-Fock equations.

       This  program  is restricted to D2h symmetry and its subgroups and the orbital occupations
       are required to be integers.  Thus, certain pure  angular  momentum  states  derived  from
       partial  occupation of degenerate orbitals cannot be obtained with the present codes.  For
       example, the 2PIu (doublet PI u) state of linear O-N-O  derived  from  the  lowest  energy
       linear  (pi  u)1  configuration  may  only  be  computed as the 2B2u (doublet B2u) or 2B3u
       (doublet B 3u) component of the 2PIu (doublet PI  u)  state,  and  the  resulting  spatial
       wavefunction  will  not have PI symmetry.  In a certain sense, however, this is desirable,
       as the energy will be a continuous function of the bending angle.  Calculating the  energy
       of bent configurations as 2B2u (doublet B 2u) or 2B3u (doublet B 3u) and doing a pure 2PIu
       (doublet PI u) state at linear geometries results in a pronounced discontinuity.

       For the most part, triplet states resulting from double occupation of a doubly  degenerate
       orbital,  such  as  the  3A2  (triplet  A  2)  state  resulting  from  the  (e')2 or (e")2
       configurations in D3h symmetry, or the 3SIGMAg (triplet SIGMA g) state of a (pi g)2 or (pi
       u)2  configuration in Dinfh (D infinity h) symmetry, will have the proper spatial symetry.
       The singlet states resulting from these  same  electronic  configurations  are  inherently
       multiconfiguration  and,  as  such,  are  not  well  represented  by  single configuration
       wavefunctions.

REFERENCES

       PK-file method:

       1.     R. C. Raffenetti, Chem. Phys. Lett. 20 (1973) 335.

       Molecular symmetry and closed shell HF calculations:

       1.     M.Dupuis, and H.F.King, Int. J. Quant. Chem.  11 (1977) 613.

       DIIS for closed shell:

       1.     P. Pulay, Chem. Phys. Lett. 73 (1980) 393.

       2.     P. Pulay, J. Comp. Chem. 3 (1982) 556.

       Coupling coefficients (alpha and beta) for open shell:

       1.     C. C. J. Roothaan, Rev. Mod. Phys. 32 (1960) 179.

       Damping:

       1.     D. R. Hartree, "The Calculation of Atomic Structures" (Wiley: New York) 1957.

       2.     M. C. Zerner and M. Hehenberger, Chem. Phys. Lett. 62 (1979) 550.

       Level shifting:

       1.     V. R. Saunders and I. H. Hillier, Int. J. Quant. Chem. 7 (1973) 699.

CONVERGING CSCF

       For difficult open shell cases,  it  is  recommended  that  an  appropriate  closed  shell
       calculation  be  run first (add or remove an extra electron) and that this SCF vector then
       be used as a guess for the desired open shell wavefunction.  For TCSCF cases, it is always
       wise  to  run  a  closed shell (or perhaps the appropriate triplet) SCF first and then use
       this as a guess for the TCSCF.

       For open shell systems, a level shift value of 0.5 to 3.0 is recommended.   Start  with  a
       high value (2.0 - 3.0) for the first SCF calculation and then reduce it (to 0.5 - 1.0) for
       subsequent runs which use a converged SCF vector as the starting point.

       It is extremely important to note that  this  version  of  the  code  no  longer  supports
       OPENTYPE.   One  must  use the new keywords REFERENCE and MULTP to specify the type of SCF
       needed.

INPUT FORMAT

       The cscf program searches through the default keyword path (first SCF  and  then  DEFAULT)
       for the following keywords:

       LABEL = string
              This  is  a character string to be included in the output.  This string is not used
              by the program.  There is no default.

       WFN = string
              This is the type of wavefunction which is ultimately desired.  The default is SCF.

       OPENTYPE is no longer supported

       REFERENCE = string
              This specifies the type of SCF calculation one wants to do.  It can be one  of  RHF
              (for  a  closed shell singlet), ROHF (for a restricted open shell calculation), UHF
              (for an unrestricted open shell  calculation),  TWOCON  (for  a  two  configuration
              singlet),  or  SPECIAL.   If  SPECIAL  is  given,  then  alpha  and  beta  coupling
              coefficients must be given with the ALPHA and BETA keywords.  The default is RHF.

       MULTP= integer
              Specifies the multiplicity of the molecule.  Default is singlet.

       CHARGE= integer
              Specifies the charge of the molecule. Defauly is 0.

       DOCC = integer_vector
              This  gives  the  number  of  doubly  occupied   orbitals   in   each   irreducible
              representation.   There  is no default.  If this is not given, CSCF will attempt to
              guess at the occupations using the core hamiltonian.

       SOCC = integer_vector
              This  gives  the  number  of  singly  occupied   orbitals   in   each   irreducible
              representation. There is no default.

       DERTYPE = string
              This  specifies  the order of derivative that is to eventually be done.  It is used
              by the scf program to determine if certain files are to be written and it  is  also
              used  to  determine  the  default  convergence of the wavefunction.  The default is
              FIRST.

       MAXITER = integer
              This gives the maximum number of iterations.  The default is 40.

       CONVERGENCE = integer
              This specifies how tightly the wavefunction  will  be  converged.   Convergence  is
              determined  by  comparing  the  RMS change in the density matrix ("delta P") to the
              given value.  The convergence criterion is 10**(-integer).  The  default  is  7  if
              both DERTYPE = NONE and WFN = SCF are given and 10 otherwise.

       LEVELSHIFT = real
              This specifies the level shift. The default is 1.

       DIRECT =  boolean
              Specifies whether to do the SCF calculation with an integral direct technique.  The
              default is false.

       PRINT_MOS =  boolean
              Specifies whether to print the molecular orbitals or not.  The default is false.

       There are also a large number of less commonly used  input  parameters.   If  you  do  not
       understand what the following options mean, then make sure that they do not appear in your
       input.  The defaults will work in the overwhelming majority of cases.  These are specified
       with the following keywords:

       DELETE_INTS = boolean
              Integrals  files will be erased if WFN = SCF and DERTYPE = FIRST or DERTYPE = NONE.
              If you wish to keep integrals files then set DELETE_INTS = false.  The  default  is
              true.

       REORDER = string
              The parameter controls reordering of molecular orbitals.  If set to BEFORE then the
              guess orbitals from checkpoint file will be reordered. If set to  AFTER,  converged
              orbitals  will be reordered before being written to the checkpoint file.  In either
              case MOORDER parameter must be given to specify the reordering map. The default  is
              not to reorder orbitals.

       MOORDER = integer_vector
              This  specifies  a  molecular  orbital  reordering vector.  It will only be used if
              REORDER is set.  This vector maps every orbital to its new index, e.g. MOORDER = (0
              2  1) specifies that after reordering orbitals 1 and 2 will be swapped. The rank of
              this vector is the same as the number of MOs.  The  indices  are  in  Pitzer  order
              (ordered  by  symmetry,  then  by energy within each symmetry block), base-0.  CSCF
              will likely fail if the given MOORDER mixes orbitals from different  irreps.  There
              is no default.

       ALPHA = real_vector
              If  OPENTYPE  = SPECIAL, then this parameter gives the alpha coupling coefficients.
              The number of elements in this vector is MM(MM+1)/2, where  MM  is  the  number  of
              irreducible  representations  containing singly occupied molecular orbitals.  There
              is no default.

       BETA = real_vector
              If OPENTYPE = SPECIAL, then this parameter gives the  beta  coupling  coefficients.
              The  number  of  elements  in  this vector is MM(MM+1)/2, where MM is the number of
              irreducible representations containing singly occupied molecular  orbitals.   There
              is no default.

       GUESS = string
              This  option determines the type of initial guess at the eigenvector CSCF will use.
              The only valid option at the moment are : (1) GUESS = CORE, which causes it to  use
              core  Hamiltonian  eigenvector  to  start  the  calculation; (2) GUESS = AUTO which
              results in an attempt to use the MO vector in the checkpoint file,  or  resorts  to
              core guess if there is no eigenvector in that file. The default if AUTO.

       IPRINT = integer
              This is a print option.  The default is 0.

       MO_OUT = boolean
              Prints  out  the  orbitals  with  symmetry  and  occupations  at  the  end  of  the
              calculation.  Default is true.

       ROTATE = boolean
              The molecular orbitals will not be rotated if this is  false.   The  rotation  only
              affects  the  virtual orbitals for open shell systems.  This parameter must be true
              for correlated gradients and it must be false for second  and  higher  derivatives.
              The default is false if WFN = SCF and true otherwise.

       CHECK_ROT = boolean
              Check  the  molecular orbital rotation described above to ensure that no columns of
              the SCF eigenvector matrix are swapped by the rotation.  Has no effect if ROTATE  =
              false.  The default is true.

       CHECK_MO_ORTHOGONALITY = boolean
              Check  if  the  molecular orbitals are orthonormal. Useful for debugging only.  The
              default is false.

       DIIS = boolean
              This determines whether diis will be used.  The default is true.

       DIISSTART = integer
              This gives the first iteration for which DIIS will be used.  The default is 0.

       NDIIS = integer
              This gives the number of error matrices to use in the diis procedure.  The  default
              is 6 for closed shell, 4 for open shell, and 3 for tcscf.

       DIISDAMP = real
              This  gives  the  damping  factor  for  the diis procedure.  The default is 0.0 for
              closed shell, 0.02 for open shell, and 0.01 for tcscf.

       INCR = real
              This is used in tcscf to determine how often the ci coefficients are  recalculated.
              A  small  number  (~0.25)  will  cause  them  to  be  recalculated nearly every scf
              iteration.  The default is 0.25.

       DYN_ACC =  boolean
              When performing direct scf this specifies whether dynamic integral accuracy cutoffs
              will  be  used.   Default  is  true  (use dynamic cutoffs).  Initial iterations are
              performed with integrals accurate to six digits.  After  density  is  converged  to
              10^-5  or  30  iterations  are  completed,  full integral accuracy is used.  If scf
              convergence problems are experienced disabling  dynamic  cutoffs  by  setting  this
              variable to false might help.

       ORTHOG_ONLY =  boolean
              Sometimes  in  CASSCF  or  other  non-HF/KS schemes for orbital optimization, it is
              useful to reorthogonalize MO's from other geometries for the  current  geometry  so
              they  can  be  used as an initial guess for the new MO's.  This can be performed by
              running CSCF with ORTHOG_ONLY = true.  After the orbitals are  orthogonalized,  the
              program  will  quit  without  performing  an SCF computation.  This keyword will be
              ignored if there are no previous orbitals in the checkpoint file.  Defaults to true
              if WFN = DETCAS.

                                           30 May, 1991                                   cscf(1)