Relativistic many-body calculations of energies of n = 3 states for beryllium isoelectronic sequence

Energies of the 2s3s (1S0, 3S1), 2s3p (1P1, 3PJ), 2s3d (1D2, 3DJ), 2p3s (1P1, 3PJ), 2p3p (1S0, 3S1, 1P1, 1D2, 3PJ, 3DJ) and 2p3d (1P1, 1D2, 1F3, 3PJ, 3DJ, 3FJ) states of Be-like ions with nuclear charges Z = (4, 5,..., 30, 54) are determined to second order in relativistic many-body perturbation theory. Both the Coulomb interaction and the Breit interaction are included. Corrections for the frequency-dependent Breit interaction are taken into account in lowest order; corrections for the Lamb shift are also estimated and included. Comparisons with experiment and with other theoretical calculations are made. For ions with low nuclear charge, we obtain excellent agreement for the term-splitting. Results for the 2p-3d excitation energy of Xe+50 also agree very well with experimental measurements.