MOLPRO

16 THE SCF PROGRAM 98
16 THE SCF PROGRAM
The Hartree-Fock self-consistent field program is invoked by one of the following commands:
HF or RHF
UHF or UHF-SCF,options
calls the spin-restricted Hartree-Fock program
calls the spin-unrestricted Hartree-Fock program
In contrast to older versions of MOLPRO, the HF and RHF directives have identical functionality
and can both be used for closed-shell or open-shell calculations. Other aliases are HF-SCF or
RHF-SCF.
Often, no further input is necessary. By default, the number of electrons is equal to the nuclear
charge, the wavefunction is assumed to be totally symmetric (symmetry 1), and the spin multiplicity
is 1 (singlet) for an even number of electrons and 2 (doublet) otherwise. The Aufbau
principle is used to determine the occupation numbers in each symmetry. Normally, this works
well in closed-shell cases, but sometimes wrong occupations are obtained or the wavefunction
alternates between different orbital spaces. In such cases, the OCC directive must be used to
force convergence to the desired state. The default behaviour can be modified either by options
on the command line, or by directives.
In open-shell cases, we recommend to use the WF, OCC, CLOSED, or OPEN cards to define the
wavefunction uniquely. Other commands frequently used are START and ORBITAL (or SAVE)
to modify the default records for starting and optimized orbitals, respectively. The SHIFT
option or directive allows to modify the level shift in the RHF program, and EXPEC to calculate
expectation values of one-electron operators (see section 6.13).
Density fitting can be used for closed and open-shell spin-restricted HF and is involked by a
prefix DF- (DF-HF or DF-RHF, see section 15). For UHF, only Coulomb fitting is possible
(CF-UHF). Density fitting very much speeds up calculations for large molecules. The greatest
savings are seen for large basis sets with high angular momentum functions. For details see R.
Polly, H.-J. Werner, F. R. Manby, and Peter J. Knowles, Fast Hartree-Fock theory using local
density fitting approximations, Mol. Phys. 102, 2311 (2004). All publications resulting from
DF-HF or DF-KS calculations should cite this work.
16.1 Options
In this section the options for HF|RHF|UHF are described. For further options affecting Kohn-
Sham caluculations see section 17. For compatibility with previous MOLPRO versions, options
can also be given on subsequent directives, as described in later sections.
16.1.1 Options to control HF convergence
ACCU[RACY]=accu
ENERGY=thrden
START=record
SAVE|ORBITAL=record
Convergence threshold for the density matrix (square sum of
the density matrix element changes). Tf accu> 1, a threshold of
10 − accu) is used. The default depends on the global ENERGY
threshold.
The convergence threshold for the energy. The default depends
on the global ENERGY threshold.
Record holding start orbitals.
Dump record for orbitals.