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Manuscript Title: Determination of interacting configurations.
Authors: D. Ridder
Program title: INTERACTING CONFIGURATIONS
Catalogue identifier: ACFZ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 31(1984)423
Programming language: Fortran.
Computer: SUPERBRAIN.
Operating system: CP/M, VMS.
RAM: 40K words
Word size: 8
Keywords: Atomic physics, Structure, Configuration Interaction, Ls-coupling, Complex atoms.
Classification: 2.1.

Nature of problem:
Within the framework of Hartree-Fock theory, the atomic structure of states with few electrons (or equivalently few vacancies) in addition to closed shells is best described by a 'mixture' of configurations. The corresponding wavefunction is then constructed as a superposition of coupled configuration state functions involving orbital functions from a given basis set. The purpose of this program is to select the corresponding configurations that may interact with a given reference configuration.

Solution method:
The user first defines the basis set of orbitals from which the interacting configurations are formed. He can not only select the orbitals to enter the process but can also limit the maximum number of electrons fro each orbital. As an alternative, he may use a default orbital basis set. Next the referance-configuration to be considered is entered and the program calculates all possible LS-terms. From this set, one term may be selected for the case under study. Then the program forms all possible combinations of orbitals with the same number of electrons from the orbital basis set and selects those which fulfill the conditions for configuration interaction. As a result, a list of these configurations together with a zero order energy estimate is output.

Restrictions:
The maximum number of orbitals in the basis set is limited to 10. When performing the angular coupling of all shells the number of possible terms may be abundant (e.g. for configurations with many open shells). Hence, this number is at most 259, and a warning is output when this number is reached. The maximum for the number of interacting configurations is set to be 50. Up to 9 orbitals may be chosen for the reference-configuration. This is also the maximum for the interacting configurations. Only configurations having direct configuration interaction with the reference-configuration (i.e. differing in at most 2 electrons) can be treated. It is not intended to derive a whole complex of interacting configurations where sequences as the following occur: 3s03p6 - 3s3p43d - 3s23p23d2. To derive this, two calculations will be necessary. So, a complex may be generated in several runs of the program, each one producing only information on nextneighbours in the complex.

Running time:
The typical running time on the SUPERBRAIN for the test-case is 70 s, measured from the end of the interactive input (where the user action mainly determines the necessary time) until the output of the table of results.