We have used third-order perturbation theory to calculate the effect of the Breit-Pauli relativistic interaction on the dipole polarizability of ${\mathrm{Li}}^{+}$ ions of order ${\mathrm{\alpha }}^2$ . Results are in good agreement with the value obtained by Johnson and Cheng [Phys. Rev. A 53, 1375 (1996)]. In addition, the retardation (Casimir) corrections to singly excited (${1\mathrm{s}}^2$ NL) states of neutral lithium have been computed. When both of these corrections are added to the previously calculated Rydberg state energies, 1σ agreement is found with experiment [N. E. Rothery et al., Phys. Rev. A 51, 2919 (1995)]. Addition of radiative (Lamb-shift) corrections produces essentially exact agreement.

• Received 10 October 1996

DOI:https://doi.org/10.1103/PhysRevA.55.1842