$SCF
$SCF group relevant if SCFTYP = RHF, UHF, or ROHF,
required if SCFTYP = GVB)
This group of parameters provides additional control
over the RHF, UHF, ROHF, or GVB SCF steps. It must be
used for GVB open shell or perfect pairing wavefunctions.
- DIRSCF
- = a flag to activate a direct SCF calculation,
which is implemented for all the Hartree-Fock
type wavefunctions: RHF, ROHF, UHF, and GVB.
This keyword also selects direct MP2 computation.
The default of .FALSE. stores integrals on disk
storage for a conventional SCF calculation.
- FDIFF
- = a flag to compute only the change in the Fock
matrices since the previous iteration, rather
than recomputing all two electron contributions.
This saves much CPU time in the later iterations.
This pertains only to direct SCF, and has a
default of .TRUE. This option is implemented
only for the RHF, ROHF, UHF cases.
Cases with many diffuse functions in the basis
set sometimes oscillate at the end, rather than
converging. Turning this parameter off will
normally give convergence.
---- The next flags affect convergence rates.
- EXTRAP
- = controls Pople extrapolation of the Fock matrix.
- DAMP
- = controls Davidson damping of the Fock matrix.
- SHIFT
- = controls level shifting of the Fock matrix.
- RSTRCT
- = controls restriction of orbital interchanges.
- DIIS
- = controls Pulay's DIIS interpolation.
- SOSCF
- = controls second order SCF orbital optimization.
(default=.TRUE. for RHF, Abelian group ROHF, GVB)
(default=.FALSE. for UHF, non-Abelian group ROHF)
- DEM
- = controls direct energy minimization, which is
implemented only for RHF. (default=.FALSE.)
defaults for |
EXTRAP |
DAMP | SHIFT |
RSTRCT |
DIIS | SOSCF |
ab initio: |
T |
F |
F |
F |
T |
T/F |
semiempirical: |
T |
F |
F |
F |
F |
F |
The above parameters are implemented for all SCF
wavefunction types, except that DIIS will work for GVB
only for those cases with NPAIR=0 or NPAIR=1. If both
DIIS and SOSCF are chosen, SOSCF is stronger than DIIS,
and so DIIS will not be used.
Once either DIIS or SOSCF are initiated, any other
accelerator in effect is put in abeyance.
---- These parameters fine tune the various convergers.
- NCONV
- = n SCF density convergence criteria.
Convergence is reached when the density change
between two consecutive SCF cycles is less than
10.0**(-n) in absolute value. One more cycle
is executed after reaching convergence. Less
accuracy in NCONV gives questionable gradients.
(default is n=5, except CI or MP2 gradients n=6)
- SOGTOL
- = second order gradient tolerance. SOSCF will be
initiated when the orbital gradient falls below
this threshold. (default=0.25 au)
- ETHRSH
- = energy error threshold for initiating DIIS. The
DIIS error is the largest element of e=FDS-SDF.
Increasing ETHRSH forces DIIS on sooner.
(default = 0.5 Hartree)
- MAXDII
- = Maximum size of the DIIS linear equations, so
that at most MAXDII-1 Fock matrices are used
in the interpolation. (default=10)
- DEMCUT
- = Direct energy minimization will not be done
once the density matrix change falls below
this threshold. (Default=0.5)
- DMPCUT
- = Damping factor lower bound cutoff. The damping
damping factor will not be allowed to drop
below this value. (default=0.0)
note: The damping factor need not be zero to achieve
valid convergence (see Hsu, Davidson, and
Pitzer, J.Chem.Phys., 65, 609 (1976), see
especially the section on convergence control),
but it should not be astronomical either.
For more info on the convergence methods,
see the 'Further Information' section.
----- miscellaneous options -----
- UHFNOS
- = flag controlling generation of the natural
orbitals of a UHF function. (default=.FALSE.)
- MVOQ
- = 0 Skip MVO generation (default)
- = n Form modified virtual orbitals, using a cation
with n electrons removed. Implemented for
RHF, ROHF, and GVB. If necessary to reach a
closed shell cation, the program might remove
n+1 electrons. Typically, n will be about 6.
- NPUNCH
- = SCF punch option
- = 0 do not punch out the final orbitals
- = 1 punch out the occupied orbitals
- = 2 punch out occupied and virtual orbitals
The default is NPUNCH = 2.
----- options for virial scaling -----
- VTSCAL
- = A flag to request that the virial theorem be
satisfied. An analysis of the total energy
as an exact sum of orbital kinetic energies
is printed. The default is .FALSE.
This option is implemented for RHF, UHF, and ROHF,
for RUNTYP=ENERGY, OPTIMIZE, or SADPOINT. Related
input is as follows:
- SCALF
- = initial exponent scale factor when VTSCAL is
in use, useful when restarting. The default
is 1.0.
- MAXVT
- = maximum number of iterations (at a single
geometry) to satisfy the energy virial theorem.
The default is 20.
- VTCONV
- = convergence criterion for the VT, which is
satisfied when 2 + + R x dE/dR is less
than VTCONV. The default is 1.0D-6 Hartree.
For more information on this option, which is most
economically employed during a geometry search, see
M.Lehd and F.Jensen, J.Comput.Chem. 12, 1089-1096(1991).
The next parameters define the GVB wavefunction. Note
that ALPHA and BETA also have meaning for ROHF. See also
MULT in the $CONTRL group. The GVB wavefunction assumes
orbitals are in the order core, open, pairs.
- NCO
- = The number of closed shell orbitals. The
default almost certainly should be changed!
(default=0).
- NSETO
- = The number of sets of open shells in the
function. Maximum of 10. (default=0)
- NO
- = An array giving the degeneracy of each open
shell set. Give NSETO values.
(default=0,0,0,...).
- NPAIR
- = The number of geminal pairs in the -GVB-
function. Maximum of 12. The default
corresponds to open shell SCF (default=0).
- CICOEF
- = An array of ordered pairs of CI coefficients
for the -GVB- pairs. For example, a two pair
case for water, say, might be
CICOEF(1)=0.95,-0.05,0.95,-0.05. If not
normalized, as in the default, they will be.
This parameter is useful in restarting a GVB
run, with the current CI coefficients.
(default = 0.90,-0.20,0.90,-0.20,...)
- COUPLE
- = A switch controlling the input of F, ALPHA,
and BETA. The default is to use internally
stored values for these variables. Note
ALPHA and BETA can be given for -ROHF-, as
well as -GVB-. (Default=.FALSE.)
- F
- = An vector of fractional occupations.
- ALPHA
- = An array of A coupling coefficients given in
lower triangular order.
- BETA
- = An array of B coupling coefficients given in
lower triangular order.
Note: The default for F, ALPHA, and BETA depends on
the state chosen. Defaults for the most commonly occuring
cases are internally stored.
For more discussion of GVB/ROHF input
see the 'further information' section
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