LS-term dependence of Slater integrals in pnp' configurations. I. Hartree-Fock calculations for individual terms of the np⁵n'p configurations in the Ne I and Ar I isoelectronic sequences

Hartree-Fock calculations are reported for individual terms of np 5 (n+1)p configurations in the Ne I (NwI, Na II, Mg III) and Ar I (Ar I, K II, Ca III) isoelectronic sequences with special emphasis on the 1 S term. For this term, the conventional restricted Hartree-Fock approach does not provide upper bounds to the energies, because of mixing with the np 6 1 S groundstate. Orthogonality to the groundstate has been introduced explicitly in the calculations. It is shown that, although this procedure provides upper bounds for the energies, the absolute errors are larger than in the conventional approach. Non-diagonal energy parameters are of importance in the calculations, especially for 1 S. For the 1 S term in Ne I, the epsilon 3p,2p parameter is larger than the diagonal epsilon 3p,2p parameter. This appears to be the first time such a case has been reported. The size of the non-diagonal energy parameters necessitated some modifications of the calculational procedure.