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Manuscript Title: A program system for ab initio MO calculations on vector and parallel processing machines. Part 2: SCF closed-shell and open-shell iterations.
Authors: M.-M. Rohmer, J. Demuynck, M. Benard, R. Wiest, C. Bachmann, C. Henriet, R. Ernenwein
Catalogue identifier: ABRR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 60(1990)127
Programming language: Fortran.
Computer: CRAY-2.
Operating system: UNICOS 4.0.
Word size: 64
Peripherals: disc.
Keywords: Molecular orbitals, Mo, Ab initio, Scf, Closed-shell, Open-shell, Vectorization, Cray-2, Integral.
Classification: 16.10.

Subprograms used:
Cat Id Title Reference
ABRB_v1_0 ASTERIX-INTEGS CPC 58(1990)305

Nature of problem:
Iterative solution of the Schrodinger equation for molecules in the Restricted Hartree-Fock approximation, using the formalism developed by Roothaan for closed-shell and open-shell configurations.

Solution method:
A file of semi-ordered P supermatrix elements (or P and Q supermatrix elements in the open-shell case) is generated from the file of two- electron repulsion integrals. The supermatrix file is iteratively processed in a vector loop to build the electron repulsion matrix. The convergence of the SCF iterations is automatically controlled through level-shifting techniques.

These programs are part of the ASTERIX package. It is assumed that the input files have been created by ASTERIX-INTEGS (see part 1 of this series). The size of the CGTO basis set is limited to 330 functions in order to keep the high speed storage below 40 * 10**6 words. The size can be increased by just modifying the proper PARAMETER statement. The open-shell program is restricted to configurations with identical populations and equivalent spin contributions for all open-shell orbitals.

Unusual features:
Same as for the calculation of two-electron integrals (see Part 1). Multitasking has however not been implemented in the present programs.

Running time:
The time for generating 10**7 supermatrix elements is about 3 seconds. All supermatrix elements must be generated. Those elements that are either below the rejection threshold or unnecessary because of symmetry are then dropped. The remaining elements are stored. In the subsequent SCF iterations, the processing of 10**7 stored elements requires about 0.9s for the closed-shell case and 1.7s for the open-shell case.