$GUESS

$GUESS group (optional, relevant for all SCFTYP's)

This group controls the selection of initial molecular orbitals.

GUESS
= Selects type of initial orbital guess.

= HUCKEL Carry out an extended Huckel calculation using a Huzinaga MINI basis set, and project this onto the current basis. This is implemented for atoms up to Rn, and will work for any all electron or ECP basis set. (default for most runs)

= HCORE Diagonalize the one electron Hamiltonian to obtain the initial guess orbitals. This method is applicable to any basis set, but does not work as well as the HUCKEL guess.

= MOREAD Read in formatted vectors punched by an earlier run. This requires a $VEC group, and you MUST pay attention to NORB below.

= MOSAVED (default for restarts) The initial orbitals are read from the DICTNRY file of the earlier run.

= SKIP Bypass initial orbital selection. The initial orbitals and density matrix are assumed to be in the DICTNRY file.

All GUESS types except 'SKIP' permit reordering of the orbitals, carry out an orthonormalization of the orbitals, and generate the correct initial density matrix. The initial density matrix cannot be generated for -CI- and -MCSCF-, so property restarts for these wavefunctions will require 'SKIP' which is an otherwise seldom used option. Note that correct computation of a -GVB- density matrix requires CICOEF in $SCF. Another possible use for 'SKIP' is to speed up a EXETYP=CHECK job, or a RUNTYP=HESSIAN job where the hessian is supplied.

PRTMO
= a flag to control printing of the initial guess. (default=.FALSE.)

NORB
= The number of orbitals to be read in the $VEC group. This applies only to GUESS=MOREAD.

For -RHF-, -UHF-, -ROHF-, and -GVB-, NORB defaults to the number of occupied orbitals. NORB must be given for -CI- and -MCSCF-. For -UHF-, if NORB is not given, only the occupied alpha and beta orbitals should be given, back to back. Otherwise, both alpha and beta orbitals must consist of NORB vectors.
NORB may be larger than the number of occupied MOs, if you wish to read in the virtual orbitals. If NORB is less than the number of atomic orbitals, the remaining orbitals are generated as the orthogonal complement to those read.

NORDER
= Orbital reordering switch.

= 0 No reordering (default)

= 1 Reorder according to IORDER and JORDER.

IORDER
= Reordering instructions.
Input to this array gives the new molecular orbital order. For example, IORDER(3)=4,3 will interchange orbitals 3 and 4, while leaving the other MOs in the original order. This parameter applies to all orbitals (alpha and beta) except for -UHF-, where it only affects the alpha MOs. (default is IORDER(i)=i )

JORDER
= Reordering instructions.
Same as IORDER, but for the beta MOs of -UHF-.

TOLZ
= level below which MO coefficients will be set to zero. (default=1.0E-7)

TOLE
= level at which MO coefficients will be equated. This is a relative level, coefficients are set equal if one agrees in magnitude to TOLE times the other. (default=5.0E-5)

MIX
= rotate the alpha and beta HOMO and LUMO orbitals so as to generate inequivalent alpha and beta orbital spaces. This pertains to UHF singlets only. (default=.FALSE.)


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