Many-body calculation of the 2p1/2,3/2-2s1/2transition energies in Li-likeU238

We present a relativistic many-body calculation of the 2${\mathit{s}}_{1/2}$ and 2${\mathit{p}}_{1/2,3/2}$ ionization energies in Li-like ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$, based on the coupled-cluster singles and doubles approximation with the inclusion of the unretarded Breit interaction, using Dirac-Fock-Breit orbitals. A detailed comparison is made with a similar calculation using ordinary Dirac-Fock orbitals. The calculation yields the transition energies, and by comparison with the recently published experimental values we find the value for the remaining quantum-electrodynamical correction, which is compared with recent Lamb-shift calculations. The importance of an accurate nuclear model for evaluating the nuclear-size effect is also discussed.