*SCF INPUT

Purpose:

This section deals with the closed shell, one open shell and high-spin spin-restricted Hartree-Fock cases and Kohn-Sham DFT. The input here will usually only be used if either ".DFT" or ".HF" has been specified under "**WAVE FUNCTIONS" (though it is also needed for MP2 calculations based on saved closed-shell HF orbitals). Single configuration cases with more than one open shell are handled by the general *CONFIGURATION INPUT section, although high-spin restricted open-shell Hartree-Fock or Kohn-Sham DFT calculations can be done using the ".HSROHF" described here.

.AUTOCCUPATION

Default for SCF calculations starting from Hückel or H1DIAG starting orbitals.

Allow the distribution of the Hartree-Fock occupation numbers over symmetries to change based on changes in orbital ordering during DIIS optimization. This keyword is incompatible with ".HSROHF" and ".COREHOLE", or if the HF calculation is followed by CI or MCSCF..

.C2DIIS

Use Harrell Sellers' C2-DIIS algorithm instead of Pulay's C1-DIIS algorithm (see comments).

.COREHOLE

READ (LUINP,*) JCHSYM,JCHORB
JCHSYM = symmetry of core orbital
JCHORB = the orbital in symmetry JCHSYM with a single core hole
Single core hole open shell RHF calculation, ".OPEN SHELL" must not be specified. The specified core orbital must be inactive. The number of doubly occupied orbitals in symmetry JCHSYM will be reduced with one and instead an open shell orbital will be added for the core hole orbital. If the specified core orbital is not the last occupied orbital in symmetry JCHSYM it will switch places with that orbital and user-defined reordering is not possible. If explicit reordering is required you must also reorder the core orbital yourself and let JCHORB point to the last occupied orbital of symmetry JCHSYM. See comments below.

.CORERELAX

(ignored if ".COREHOLE" isn't also specified)
Optimize core hole state with relaxed core orbital using Newton-Raphson algorithm. It is assumed that this calculation follows an optimization with frozen core orbital and the specific value of "JCHORB" under ".COREHOLE" is ignored (no reordering will take place).

.DOUBLY OCCUPIED

READ (LUINP,*) (NRHF(I),I=1,NSYM)
Explicit specification of number of doubly occupied orbitals in each symmetry for DFT, RHF and MP2 calculations. This keyword is required when Hartree-Fock or MP2 is part of a multistep calculation which includes an MCSCF wave function. Otherwise the program by default will try to guess the occupation, corresponding to the ".AUTOCC" keyword.

.ELECTRONS

READ (LUINP,*) NRHFEL
Number of electrons in the molecule. By default, this number will be determined on the basis of the nuclear charges and the total charge of the molecule as specified in the MOLECULE.INP file. The keyword is incompatible with the keywords ".DOUBLY OCCUPIED", ".OPEN SHELL", and ".HSROHF".

.FC MVO

READ (LUINP,*) (NMVO(I), I = 1,NSYM)
Modified virtual orbitals using Bauschlichers suggestion (see Ref. [150]) for CI or for start guess for MCSCF. The modified virtual orbitals are obtained by diagonalizing the virtual-virtual block of the Fock matrix constructed from NMVO(1:NSYM) doubly occupied orbitals. The occupied SCF orbitals (i.e those specified with ".DOUBLY OCCUPIED" and ".OPEN SHELL" or by automatic occupation) are not modified. The construction of modified virtual orbitals will follow any SCF and MP2 calculations. See comments below.

.FOCK ITERATIONS

READ (LUINP,*) MAXFCK
Maximum number of closed-shell Roothaan Fock iterations (default = 0).

.FROZEN CORE ORBITALS

READ (LUINP,*) (NFRRHF(I),I=1,NSYM)
Frozen orbitals per symmetry (if MP2 follows then at least these orbitals must be frozen in the MP2 calculation). NOTE: no Roothaan Fock iterations allowed if frozen orbitals.

.H1VIRT

Use the virtual orbitals that diagonalize the one-electron Hamiltonian operator.

.HSROHF

READ (LUINP,*) (NROHF(I),I=1,NSYM)
High spin restricted open-shell Hartree-Fock. Specify the number of singly occupied orbitals in each irreducible representation of the molecular point group. Only the high-spin state of these singly-occupied orbitals will be made and used in the calculations.

.MAX DIIS ITERATIONS

READ (LUINP,*) MXDIIS
Maximum number of DIIS iterations (default = 60).

.MAX ERROR VECTORS

READ (LUINP,*) MXEVC
Maximum number of DIIS error vectors (default = 10, if there is sufficient memory available to hold these vectors in memory).

.MAX MACRO ITERATIONS

READ (LUINP,*) MXHFMA
Maximum number of QCSCF macro iterations (default = 15).

.MAX MICRO ITERATIONS

READ (LUINP,*) MXHFMI
Maximum number of QCSCF micro iterations per macro iteration (default = 12).

.NODIIS

Do not use DIIS algorithms (default: use DIIS algorithm).

.NONCANONICAL

No transformation to canonical orbitals.

.NOQCSCF

No quadratically convergent SCF iterations. Default is to switch to QCSCF if DIIS doesn't converge.

.OPEN SHELL

Default = no open shell
READ (LUINP,*) IOPRHF
Symmetry of the open shell in a one open shell calculation. See also ".HSROHF" for high-spin ROHF with more than one singly occupied orbital.

.PRINT

READ (LUINP,*) IPRRHF
Resets general print level to IPRRHF in Hartree-Fock calculation (if not specified, global print levels will be used).

.SHIFT

READ (LUINP,*) SHFTLVL
Initial value of level-shift parameter in DIIS iterations. The default value is 0.0D0 (no level shift). May be tried if convergence problems in DIIS. The value is added to the diagonal of the occupied part of the Fock matrix before Roothaan diagonalization, reducing the mixing of occupied and virtual orbitals (step restriction). NOTE that the value should thus be negative. The DIIS routines will automatically invoke level-shifting (step restriction) if DIIS seems to be stalling.

.THRESH

Default = 1.0D-06
READ (LUINP,*) THRRHF
Hartree-Fock convergence threshold for energy gradient. The convergence of the energy will be approximately the square of this number.

Comments:

By default, the RHF/DFT part of a calculation will consist of :

1. MAXFCK Roothaan Fock iterations (early exit if convergence or oscillations). However, the default is that no Roothaan Fock iterations are done unless explicitly requested through the keyword ".FOCK I".
2. MXDIIS DIIS iterations (exit if convergence, i.e. gradient norm less than THRRHF, and if convergence rate too slow or even diverging).
3. Unless NOQCSCF, quadratically convergent Hartree-Fock/DFT until gradient norm less than THRRHF.
4. If ".FC MVO" has been specified then the virtual SCF orbitals will be modified by diagonalizing the virtual-virtual block of a modified Fock matrix: the Fock matrix based on the occupied orbitals specified after the keyword, a good choice is the inactive (doubly occupied) orbitals in the following CI or MCSCF. The occupied SCF orbitals will not be modified. If the RHF calculation is followed by a CI or an MCSCF calculation, ".FC MVO" will usually provide much better start orbitals than the canonical orbitals (canonical orbitals will usually put diffuse, non-correlating orbitals in the active space).
   WARNING: if both ".MP2" and ".FC MVO" are specified, then the MP2 orbitals will be destroyed and replaced with ".FC MVO" orbitals.

In general ".DOUBLY OCCUPIED" should be specified for CI or MCSCF wave function calculations - you anyway need to know the distribution of orbitals over symmetries to specify the "*CI INPUT" input. For RHF or MP2 calculations the orbital occupation will be determined on the basis of the nuclear charges and molecular charge of the molecule as specified in the MOLECULE.INP file.

By default, starting orbitals and initial orbital occupation will be determined automatically on the basis of a Hückel calculation (for molecules where all nuclear charges are less than or equal to 36), corresponding to the ".AUTOCC" keyword. If problems is experienced due to the Hückel starting guess, it can be avoided by requiring another set of starting orbitals (e.g. H1DIAG).

It is our experience that it is usually most efficient not to perform any Roothaan Fock iterations before DIIS is activated, therefore, MAXFCK = 0 as default. The algorithm described in Harrell Sellers, Int. J. Quant. Chem. 45, 31-41 (1993) is also implemented, and may be selected with ".C2DIIS".

FC MVO: This option can be used without a Hartree-Fock calculation to obtain compact virtual orbitals, but ".DOUBLY OCCUPIED" must be specified anyway in order to identify the virtual orbitals to be transformed.

COREHOLE: Enable SCF single core-hole calculations. To perform an SCF core hole calculation just add the ".COREHOLE" keyword to the input for the closed-shell RHF ground state calculation, specifying from which orbital to remove an electron, and provide the program with the ground state orbitals using the appropriate ".MOSTART" option (normally NEWORB). Note that this is different from the MCSCF version of ".COREHOLE" under "*OPTIMIZATION" (p. ); in the MCSCF case the user must explicitly move the core hole orbital from the inactive class to RAS1 by modifying the "*CONFIGURATION INPUT" (p. ) specifications between the initial calculation with filled core orbitals and the core hole calculation. The core hole orbital will be frozen in the following optimization. After this calculation has converged, the CORERELAX option may be added and the core orbital will be relaxed. When CORERELAX is specified it is assumed that the calculation was preceded by a frozen core calculation, and that the orbital has already been moved to the open shell orbital. Only the main peak can be obtained in SCF calculations, for shake-up energies MCSCF must be used.