Atomic Bethe-Goldstone calculations of term splittings, ionization potentials, and electron affinities. III. Al, Si, P, S, Cl, and Ar using orbital excitations

Ionization potentials, electron affinities, and term splittings have been computed for the lowest electronic configurations of atoms with $Z$ from 13 to 18. Following approximate Hartree-Fock calculations, correlation energies are computed by variational solution of one- and two-electron Bethe-Goldstone equations, defined in terms of orbital excitations. All computed energy differences are in good agreement with experiment. The energy differences arise primarily from $M$-shell correlations, with very little contribution from $L-M$ interactions, and no substantial $L$-shell effect. Estimates are made of the effects of extending the orbital basis set beyond $f$ orbitals and of including three-particle correlation.