Relativistic many-body calculations of the energies of<i>n</i>=2 states for the berylliumlike isoelectronic sequence

Abstract

Energies of the ten (2l2${\mathit{l}}^{\ensuremath{'}}$) states of ions of the beryllium isoelectronic sequence are determined to second order in relativistic many-body perturbation theory. Both the second-order Coulomb interaction and the second-order Breit-Coulomb interaction are included. Corrections for the frequency-dependent Breit interaction are taken into account in lowest order only. The effect of the Lamb shift is also estimated and included. Comparison with experiment and other theoretical data is made. \textcopyright{} 1996 The American Physical Society.