********************************************************************************
*                                                                              *
*                                  2DHF                                        *
*                                                                              *
*                                                                              *
*         2-Dimensional Finite Difference Hartree-Fock program                 *
*                         for diatomic molecules                               *
*                                                                              *
*                            (version 1-2003)                                  *
*                                                                              *
*                                                                              *
*  Copyright (C) 1996 Jacek Kobus, Jacek.Kobus@phys.uni.torun.pl               *
*  Instytut Fizyki, Uniwersytet Mikolaja Kopernika                             *
*  Grudziadzka 5/7, PL-87-100 Torun, Poland                                    *
*                                                                              *
*  Copyright (C) 1996 Leif Laaksonen, Leif.Laaksonen@csc.fi                    *
*  Centre for Scientific Computing                                             *
*  Tietotie 6, P.O.Box 405, FIN-02101 Espoo, Finland                           *
*                                                                              *
*  Copyright (C) 1996 Dage Sundholm, sundholm@chem.helsinki.fi                 *
*  Department of Chemistry, University of Helsinki                             *
*  P.O. Box 55, FIN-00014 Helsinki, Finland                                    *
*                                                                              *
*  This program is free software; you can redistribute it and/or               *
*  modify it under the terms of the GNU General Public License                 *
*  as published by the Free Software Foundation; either version 2              *
*  of the License, or (at your option) any later version.                      *
*                                                                              *
*  This program is distributed in the hope that it will be useful,             *
*  but WITHOUT ANY WARRANTY; without even the implied warranty of              *
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                *
*  GNU General Public License for more details.                                *
*                                                                              *
*  You should have received a copy of the GNU General Public License           *
*  along with this program (see COPYING).                                      *
*                                                                              *
********************************************************************************


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

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.

See the following articles for the detailed description of the
program:

  L.Laaksonen, P.Pyykko, and D. Sundholm, Comp. Phys. Reports 4 (1986) 219.
  L.Laaksonen, D.Sundholm, and P.Pyykk\"o, in "Scientific Computing in
    Finland,", Eds. K. Kankaala and R. Nieminen, Research Report R1/89,
    Centre for Scientific Computing, (1989) p. 183.
  P.Pyykk\"o, in Numerical Determination of the Electronic Structure
    of Atoms, Diatomic and Polyatomic Molecules (NATO ASI Series C271) 
    Eds. M.Defranceschi and J Delhalle, p.161
  J.Kobus, Chem. Phys. Lett. 202 (1993) 7
  J.Kobus, Comput. Phys. Commun. 78 (1994) 247
  J.Kobus, L.Laaksonen, D.Sundholm, Comp. Phys.Commun. 98 (1996) 346-358 
  J.Kobus, Numerical Hartree-Fock methods for diatomic molecules,
    Handbook of Molecular Physics and Quantum Chemistry (Chichester),
    ed. S.~Wilson (Wiley, 2002)

The programming language used is Fortran 77. However, two routines
written in C are used 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 (see Makefile).

Typical running times are very case dependent - from hundreds seconds
on an ordinary workstation up to several hours/days on a supercomputer.

The current version of the program can be downloaded from
http://laaksonen.csc.fi/num2d.html. Its original version (from 1996)
can be obtained from CPC Program Library, Queen's University of
Belfast, N. Ireland.

See INSTALLATION to configure, compile and run the program.










