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Manuscript Title: Third version of a program for calculating the static interaction potential between an electron and a diatomic molecule.
Authors: G. Raseev
Program title: ONE CENTRE STATIC POTENTIAL
Catalogue identifier: ACQW_v3_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 20(1980)267
Programming language: Fortran.
Computer: IBM 370/168.
Operating system: JES 3.
RAM: 475K words
Word size: 32
Peripherals: disc.
Keywords: Quantum chemistry, Single-centre expansion, Static potential, Dipole moment, Quadrupole moment, Multipole expansion, Electron, Scattering, Molecule.
Classification: 16.5.

Revision history:
Type Tit le Reference
correction 000A CORRECTION 28/01/86 See below
adaptation 0001 PARAMETRIZED DIMENSIONS See below

Nature of problem:
The program calculates one-centre expansions for the two-centre wave function of a diatomic molecule and also the multipole expansion of its static interaction with a point charge. It is an extension to some classes of open-shell targets of the previous versions and it provides both the wave function and the potential in a form suitable for use in an electron-molecule scattering program.

Solution method:
The original two-centre wave function is assumed to have a closed or restricted open-shell representation from a LCAOMO-SCF calculation. The LCAO basis is of Slater-type centered on the two nuclei of the molecule: The atomic orbitals are expanded in Legendre polynomials around either the centre of mass, or the centre of charge or one of the two atoms. The resulting wave function once orthomnomalisation of Lowdin is used for calculating the static potential.

Restrictions:
This program is partially dynamically allocated either through an IBM 370/165 assembler subroutine or a main FORTRAN program (present version). The only restrictions are given below. Maximum number of basis functions is 50; the one centre expansion of the potential is limited to a maximum of 21 terms and the expansion of the molecular orbital is limited to 20 terms.

Running time:
For 200 mesh points, 21 atomic and 4 molecular orbitals, 15 terms in the expansion of the one-centre molecular orbital and 4 terms in the expansion of the static potential the program takes 42 s on an IBM 370/ 168.

CORRECTION SUMMARY
Manuscript Title: Errors in the three CPC versions of the program to calculate the single centre expansion of the electron diatomic-molecule static potential. (C.P.C. 20(1980)267).
Authors: L. Malegat, M. Le Dourneuf, V.K. Lan
Program title: 000A CORRECTION 28/01/86
Catalogue identifier: ACQW_v3_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 41(1986)179
Classification: 16.5.

ADAPTATION SUMMARY
Manuscript Title: Errors in the three CPC versions of the program to calculate the single centre expansion of the electron diatomic-molecule static potential.
Authors: L. Malegat, M. Le Dourneuf, V.K. Lan
Program title: 0001 PARAMETRIZED DIMENSIONS
Catalogue identifier: ACQW_v3_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 41(1986)179
Programming language: Fortran.
Classification: 16.5.

Nature of problem:
The program calculates one centre expansions for the two-centre wavefunction of diatomic molecule and for its static interaction with a point charge.

Solution method:
The molecular wavefunction is obtained from an LCAO-MO-SCF calculation, using a basis of Slater-type atomic orbitals centered on the two nuclei. These Slater orbitals are reexpanded in Lengendre polynomials about a unique centre. Single center expansions of the molecular orbitals and static interaction then follow.

Restrictions:
The original program had limitations concerning the possible n,l values of the Slater orbitals to be expanded, the number of terms in the expansions... These limits were difficult to overcome. The present adaptation makes extensions easy, owing to the use of parametrized dimensions.

Running time:
15s on NAS 9080 for 300 mesh points, 24 atomic orbitals, 1 molecular orbital, 21 terms in the expansions of the atomic and molecular orbitals, 25 terms in the expansion of the static potential.