# Variational Bethe-Goldstone calculations of atomic oscillator strengths. Be sequence

## Abstract

Atomic oscillator strengths have been computed by applying a Bethe-Goldstone hierarchy of variational calculations consistently to both initial and final states of a given transition. For the 1s2S11s2p Po1 transitions in the He isoelectronic sequence, computed fl (length) and fv (velocity) values and the corresponding transition energies are in good agreement with the accurate f values of Pekeris et al. and with observed transition energies. For the Be isoelectronic sequence, fl and fv for 1s22s2S11s22s2p Po1 are in close agreement with each other if all double virtual excitations from 1s2s2p (with respect to 1s22s2p as reference configuration) are included in the variational calculations. The agreement between computed and observed transition energies is very good. Similar results have been obtained for other valence shell excitations of Be i: 2s2p Po32p2P3, 2s2p Po12p2 D1, 2s2p Po12p2 S1. The 2p2 S1 state apparently lies slightly above the Be ii 2s threshold. The 2p2 D1 state interacts strongly with the 2s3d D1 Rydberg state. The oscillator strength is nearly zero for the Po1D1 transition. © 1976 The American Physical Society.