$MOPAC group    (relevant if GBASIS=PM3, AM1, or MNDO)
 
     This group affects only semi-empirical jobs, which are
selected in $BASIS by keyword GBASIS.
 
PEPTID = flag for peptide bond correction.
         By default a molecular mechanics-style torsion
         potential term is added for every peptide bond
         linkage found.  The intent is to correct these
         torsions to be closer to planar than they would
         otherwise be in the semi-empirical model.  Here,
         the peptide bond means any
 
                      O       H
                      \\     /
                       C----N
                      /      \
                              X
 
         One such torsion is added for O-C-N-H and one for
         O-C-N-X.  This term is parameterized as in MOPAC6.
         Default=.TRUE.
 
 
 
 
 
$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
                 core potential 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 deck,
                 and you MUST pay attention to NORB below.
      = RDMINI   Read in a $VEC deck from a converged SCF
                 calculation using GBASIS=MINI, to project
                 the MINI orbitals onto the current basis.
                 The option improves upon the Huckel guess
                 because it involves SCF orbitals, which
                 are typically easily obtained in the small
                 MINI basis.  This option doesn't work if
                 the current basis uses core potentials.
                 potentials.  The $VEC from the MINI run
                 must contain all virtual orbitals.
      = 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.  Mostly
                 used for RUNTYP=HESSIAN when the hessian
                 is being read in from the input.
The next options are less general, being for Fragment
Molecular Orbital runs, or Divide and Conquer runs:
      = FMO      Read orbitals from the DICTNRY file, from
                 previous FMO run with MODPRP=1.
      = HUCSUB   Perform a Huckel guess in each subsystem
                 of a Divide and Conquer run
      = DMREAD   Read a density matrix from a formatted $DM
                 group, produced by a previous Divide and
                 Conquer run, see NDCPRT in $DANDC.
 
    All GUESS types except 'SKIP' permit reordering of the
orbitals, carry out an orthonormalization of the orbitals,
and generate the correct initial density matrix, for RHF,
UHF, ROHF, and GVB, but note that correct computation of
the GVB density requires also CICOEF in $SCF.  The density
matrix cannot be generated from the orbitals alone for MP2,
CI, or MCSCF, so property evaluation for these should be
RUNTYP=ENERGY rather than RUNTYP=PROP using GUESS=MOREAD.
PRTMO = a flag to control printing of the initial guess.
        (default=.FALSE.)
 
PUNMO = a flag to control punching of the initial guess.
        (default=.FALSE.)
 
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.  This may require use of NOSYM=1 in $CONTRL
         depending on your situation.  (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, giving the new molecular
         orbital order.  This parameter applies to the
         common orbitals (both alpha and beta) except for
         UHF, where IORDER only affects the alpha MOs.
             Examples (let there be 10 occupied orbitals):
               transposition of HOMO and LUMO:
                    IORDER(10)=11,10
               a different transposition:
                    IORDER(10)=15 IORDER(15)=10
               a more general permutation:
                    IORDER(8)=11,8,9,10
               so the new orbital 10 is the original 9th.
         The default is IORDER(i)=i.
 
JORDER = Reordering instructions.
         Same as IORDER, but for the beta MOs of UHF.
 
INSORB = the first INSORB orbitals specified in the $VEC
         group will be inserted into the Huckel guess,
         making the guess a hybrid of HUCKEL/MOREAD.  This
         keyword is meaningful only when GUESS=HUCKEL, and
         it is useful mainly for QM/MM runs where some
         orbitals (buffer) are frozen and need to be
         transferred to the initial guess vector set,
         see $MOFRZ.  (default=0)
 
 
  * * * the next are 3 ways to clean up orbitals * * *
 
PURIFY = flag to symmetrize starting orbitals.  This is the
         most soundly based of the possible procedures.
         However it may fail in complicated groups when the
         orbitals are very unsymmetric.  (default=.FALSE.)
 
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)
 
SYMDEN = project the initial density in order to generate
         symmetric orbitals.  This may be useful if the
         HUCKEL or HCORE guess types give orbitals of
         impure symmetry (?'s present).  The procedure
         will generate a fairly high starting energy, and
         thus its use may not be a good idea for orbitals
         of the quality of MOREAD.  (default=.FALSE.)