*HF INPUT  

Purpose:

This section deals with the closed shell and one open shell Hartree-Fock cases   . The input here will usually only be used if ".HF  " (or its alias ".SCF  ") or ".MP2  "   have been specified under "**WAVE FUNCTIONS  ". Single configuration cases with more than one open shell  are handled by the general *CONFIGURATION INPUT   section.

.AUTOCCUPATION  

Default for SCF    and MP2   calculations starting from Hückel or H1DIAG starting orbitals  .

Allow the Hartree-Fock occupation   to change based on changes in orbital ordering during DIIS  optimization.

.C2DIIS  

Use Harell 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 HF occupation 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 orbtial 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).

.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 incomaptible with the keywords ".HF OCCUPATION  " and ".OPEN SHELL  ".

.FC MVO  

See Ref. [79].

.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 if frozen orbitals.

.H1VIRTUALS  

Virtual orbitals that diagonalize the one-electron Hamiltonian matrix (see comments below).

.HF OCCUPATION  

READ (LUINP,*) (NRHF(I),I=1,NSYM)
Hartree-Fock occupancy for RHF and MP2 calculations     .

.MAX DIIS ITERATIONS  

READ (LUINP,*) MXDIIS
Maximum number of DIIS iterations  (default = 30).

.MAX ERROR VECTORS  

READ (LUINP,*) MXEVC
Maximum number of DIIS error vectors  (default = 10).

.MAX MACRO ITERATIONS  

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

.MAX MICRO ITERATIONS  

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

.NODIIS  

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

.NONCANONICAL  

No transformation to canonical orbitals 

.NOQCHF  

No quadratically convergent Hartree-Fock  iterations

.OPEN SHELL  

Default = no open shell
READ (LUINP,*) IOPRHF
Symmetry of the open shell in a one open shell  calculation.

.PRINT  

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

.THRESHOLD  

Default = 1.0D-08
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 part of a SIRIUS calculation will consist of :

1. MAXFCK Roothaan Fock iterations (early exit if convergence or oscillations).
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 NOQCHF, quadratically convergent Hartree-Fock until gradient norm less than THRRHF.
4. If ".H1VIRT" then transformation of virtual orbitals to diagonalize the one-electron Hamiltonion, i.e. virtual orbitals will be defined for a bare nuclei potential. If the RHF calculation is going to be followed directly by an MCSCF calculation, ".H1VIRT" will usually provide much better start orbitals than the canonical orbitals (canonical orbitals will usually put diffuse, non-correlating orbitals in the active space). Note that if the basis set contains compact, core correlating orbitals, ".H1VIRT" will put those in the active space. WARNING: if both ".MP2" and ".H1VIRT" are specified, then the MP2 orbitals will be destroyed and replaced with H1VIRT orbitals.

In general ".HF OCCUPATION" should be specified for CI or MCSCF      wave function calculations. If not specified, the HF occupation will be the number of inactive orbitals in the MCSCF calculation (or CI calculation if no MCSCF). For SCF or MP2      calculations the Hartree-Fock 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 Hartree-Fock occupation will be determined on the basis of a Hückel  calculation (for elements with nuclear charge less than 36). If problems is experienced due to the Huckel 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  ".

H1VIRTUALS: This option can be used without a Hartree-Fock calculation to obtain compact virtual orbitals, but ".HF OCCUPATION  " must be specified anyway in order to identify the virtual orbitals to be transformed.

COREHOLE: These new options (summer 1994) are added to make SCF single core hole  calculations simple. 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 preceeded 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.