Many-body perturbation-theory calculations of energy levels along the lithium isoelectronic sequence

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Abstract
Energies of n=2 states for ions of the lithium isoelectronic sequence are calculated from Z=3–92, starting from a Hartree-Fock potential and including second- and third-order correlation corrections, the lowest-order Breit interaction with retardation treated exactly, the second-order correlation corrections to the Breit interaction, and corrections for reduced mass and mass polarization. The resulting differences between theory and experiment for the 2p fine structure and the 2s-2p splittings are found to be in rough agreement with the one-electron Lamb shift, but clear deviations can be seen. A discussion is given of the calculations required to evaluate these deviations within the framework of quantum electrodynamics.