cscf - solves the Hartree-Fock equations

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.OnemustusethenewkeywordsREFERENCEandMULTPtospecifythetypeofSCFneeded.

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.

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.

OPENTYPEisnolongersupportedREFERENCE=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=(021) 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)

Name

       cscf - solves the Hartree-Fock equations

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.