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Manuscript Title: A more efficient version of the WEIGHTS and NJSYM packages.
Authors: N.S. Scott, A. Hibbert
Program title: WEIGHTS A MORE EFFICIENT VERSION
Catalogue identifier: ACQL_v3_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 28(1982)189
Programming language: Fortran.
Computer: CRAY-1.
Operating system: OS 1.10.
RAM: 62K words
Word size: 64
Keywords: Atomic physics, Theoretical methods, Racah coefficients, Coefficients of Fractional parentage, Recoupling coefficient, Function wave, Ls coupling, Bound states, Continuum Slater integral.
Classification: 2.9.

Subprograms used:
Cat Id Title Reference
ACQB_v1_0 P SHELL C.F.P. CPC 1(1969)15
ACQC_v2_0 A NEW D SHELL C.F.P. CPC 6(1973)88
AAGD_v3_0 NJSYM - A MORE EFFICIENT VERSION CPC 28(1982)189

Nature of problem:
In configuration interaction calculations, one wishes to evaluate the matrix of the Hamiltonian operator with respect to a basis set of configuration wave functions. The more difficult part of this procedure is to determine the two-electron interaction matrix elements. These matrix elements may be written as a weighted sum of radial Slater integrals. This program calculates the coefficients of these integrals.

Solution method:
The coefficients of the Slater integrals are obtained from integration over all spin and angular coordinates and (N-2) radial coordinates, for an N-electron atom. The scheme for calculating the coefficients is described by Fano. In this scheme, the coefficients may be expressed as sums over fractional parentage coefficients, recoupling coefficients and reduced matrix elements. A more efficient package is now employed to evaluate the recoupling coefficient. This results in execution time decreasing by a factor of between three and four.

Restrictions:
Any number of electrons in s-, p- or d-shells are allowed (<=2(2l+1), but no more than two electrons in any shell of higher orbital angular momentum. The earlier over-all restriction of l<=4 is lifted in this new version. The restriction on a maximum of two electrons for l>2 may be relaxed by inclusion of further fractional parentage coefficient packages. Current dimensions restrict the number of occupied subshells to a maximum of ten.

Running time:
The test run case took 6.6 s execution time on the CRAY-1.