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Manuscript Title: A numerical Hartree-Fock program for diatomic molecules.
Authors: J. Kobus, L. Laaksonen, D. Sundholm
Program title: 2dhf
Catalogue identifier: ADEB_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 98(1996)346
Programming language: Fortran 77, Fortran 90, C.
Operating system: Unix.
Keywords: Restricted open-shell Hartree-fock-(slater) Method, Prolate spheroidal Coordinates, 8th-order discretization, Successive Overrelaxation, Multicolour successive Overrelaxation, Molecular physics, Structure.
Classification: 16.1.

Nature of problem:
The program finds virtually exact solutions of the Hartree-Fock and Hartree-Fock-Slater equations for diatomic molecules. The lowest energy eignestates of a given irreducible representation and spin can be obtained.

Solution method:
Single particle two-dimensional numerical functions (orbitals) are used to construct an antisymmetric many-electron wave function of the restricted open-shell Hartree-Fock model. The orbitals are obtained by solving the Hartree-Fock equations which are coupled two-dimensional second-order (elliptic) partial differential equations (PDE). The Coulomb and exchange potentials are obtained as solutions of the corresponding Poisson equations. The PDEs are disretized by the 8th- order central difference stencil on a two-dimensional grid (or subgrids) and the resulting large and sparse system of linear equations is solved by the (multicolour) successive overrelaxation method ((MC)SOR). The self-consistent-field iterations are interwoven with the (MC)SOR ones and orbital energies and normalization factors are used to monitor the convergence. The accuracy of solutions depends mainly on the grid and the system under consideration.

Restrictions:
The present version of the program is restricted to 60 orbitals and 3 subgrids. The number of subgrids and the maximum grid size are determined by the user before the executable of the program is made.

Unusual features:
The program uses two C routines for recording the date and time of the run and the CPU usage. Several BLAS (Basic Linear Algebra System) routines are emulated by the program. When possible they should be replaced by their library equivalents.

Running time:
Very case dependent - from a few CPU seconds on an ordinary workstation up to several hours on a supercomputer.