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Manuscript Title: A new program for calculating matrix elements in atomic structure.
Authors: P.M. Lima
Program title: COEFANG1
Catalogue identifier: ACBF_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 66(1991)99
Programming language: Fortran.
Computer: VAX 11/780.
Operating system: VAX/VMS.
RAM: 206K words
Word size: 32
Keywords: Atomic physics, Theoretical methods, Matrix elements, Electrostatic Interaction, Angular momentum, Recoupling coefficients, Coefficients of Fractional parentage, Ls-coupling.
Classification: 2.9.

Nature of problem:
To solve some problems concerning the electronic structure of atoms, one needs to evaluate the matrix elements of the Hamiltonian, including the electrostatic interaction, with respect to a basis set of configuration wave functions. These matrix elements may be expressed as weighted sums of radial Slater integrals. For a given set of configurations, the program defines which wave functions must be included in the basis set, computes all the arising coefficients of the radial integrals and, if these integrals are given, calculates the matrix elements.

Solution method:
The scheme to calculate the coefficients of the radial integrals is similar to that used by Hibbert (Comp. Phys. Commun 1(1970)359). The main difference is in the method used to calculate the recoupling coefficients, which is based on graphical techniques and was described in another paper (Comp. Phys. Commun. ). The configurations are defined just by the number of electrons in each open shell. According to the scheme of LS-coupling, the program generates all the possible sets of angular momentum parameters for the given configurations.

Restrictions:
In each run may be considered up to 15 configurations, since they comprise no more than 10 different open shells. Any number of electrons in s-, p- or d-shells are allowed, but no more than two electrons in any shell of higher orbital angular momentum. The maximal dimension of the configuration interaction matrix is 30. These parameters may be augmented, if there is enough memory in the computer.

Running time:
The time required for the test run (example 1) is 2 s.