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Manuscript Title: Diagrammatic many-body perturbation expansion for atoms and molecules: II. Second-order and third-order ladder energies.
Authors: D.M. Silver
Program title: MBPT LADDER DIAGRAMS
Catalogue identifier: ACXG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 14(1978)81
Programming language: Fortran.
Computer: IBM 360/91.
Operating system: ASP.
Program overlaid: yes
RAM: 200K words
Word size: 8
Peripherals: disc.
Keywords: Atomic physics, Molecular physics, Electronic, Structure, Diagram, Many-body, Perturbation theory, Ladder diagram, Quantum chemistry.
Classification: 2.1, 16.1.

Subprograms used:
Cat Id Title Reference
ACXF_v1_0 MBPT ORGANIZATION CPC 14(1978)71
ACXH_v1_0 MBPT RING DIAGRAMS CPC 14(1978)91

Nature of problem:
The determination of perturbative solutions to the non-relativistic Schrodinger equation for the electronic structure of atomic and molecular systems is considered within the Born-Oppenheimer approximation.

Solution method:
The diagrammatic many-body perturbation expansion is employed through third-order in the energy and first-order in the wavefunction, including all many-body effects that arise. The calculations are performed within the algebraic approximation in which eigenfunctions are parameterized by expansion in a finite set of basis functions. Computer algorithms are presented for the evaluation of second-order energies; overlap integrals over the first-order perturbative wavefunction; and third-order particle-particle and hole-hole ladder diagrams.

Restrictions:
These programs are restricted to non-degenerate, closed-shell ground- states of atoms and molecules. The reference wave-function must be a closed-shell matrix Hartree-Fock single-determinantal wavefunction. Program dimension statements limit the basis set size to 10 occupied spatial orbitals (20 electrons) and 25 unoccupied spatial orbitals (50 virtual states): these dimensions can easily be increased if neccessary.

Unusual features:
This program is an integral part of a set of programs, (Comp. Phys. Commun. 14(1978)71, 14(1978)91). This program requires input from a previous part of the set and returns its output to those routines.

Running time:
Running time depend strongly on the basis set size and on the number of occupied orbitals: some timing data have been presented. The test run requires ~0.6 s of CPU time on the IBM 360/91 for the subprogram within the domain of this paper.