Title of program: MBPT LADDER DIAGRAMS Nature of physical problem The determination of perturbative solutions of the non-relati-Catalogue number: ACXG vistic Schrodinger equation for the electronic structure of atomic and molecular systems is considered within the Born-Program obtainable from: CPC Program Library, Queen's Oppenheimer approximation. University of Belfast, N. Ireland (see application form in Method of solution this issue) The diagrammatic many-body perturbation expansion is employed through third-order in the energy and first-order Computer: IBM 360/91; Installation: The Johns Hopkins in the wavefunction, including all many-body effects that University Applied Physics Laboratory arise. The calculations are performed within the algebraic approximation [1] in which eigenfunctions are parameter-Operating system: ASP ized by expansion in a finite set of basis functions. Computer algorithms are presented for the evaluation of second-order Programming language: FORTRAN IV energies; overlap integrals over the first-order perturbative wavefunction; and third-order particle--particle and hole-hole High speed storage required: 200 kilobytes ladder diagrams. Number of bits in a byte: 8 Restrictions on the complexity of the problem These programs are restricted to non-degenerate, closed-shell Overlay structure: 4 segments, 1 node ground-states of atoms and molecules. The reference wavefunction must be a closed-shell matrix Hartree-Fock single-Number of magnetic tapes required: none determinantal wavefunction. Program dimension statements limit the basis set size to 10 occupied spatial orbitals (20 Other peripherals used: disc drives, line printer, electrons) and 25 unoccupied spatial orbitals (50 virtual states): these dimensions can easily be increased if necessary. Number of cards in combinedprogram and test deck: 794 Typical running time Qird punchingcode: IBM EBCDIC 029 Running times depend strongly on the basis set size and on the number of occupied orbitals: some timing data have been CPC Library subprograms used: presented [1,2]. The test run requires ~-0.6s of CPU time Cat. no.