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$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.
CONV = SCF density convergence criteria. Convergence is reached when the density change between two consecutive SCF cycles is less than this in absolute value. One more cycle will be executed after reaching
convergence. Less accuracy in CONV gives questionable gradients. The default is 1.0d-05, except runs involving CI or MP2 gradients use 1.0d-06.
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 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<T> + <V> + 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 ).

• GVB/ROHF options
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 occurring cases are internally stored.
For more discussion of GVB/ROHF input see here.
 

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