Model operator approach to the relativistic Lamb shift calculations in many-electron atoms and highly charged molecular ions

The quantum electrodynamics (QED) corrections to the alkali metal ionization potentials and to the ground-state energy of the ${\text{U}}^{92+}-{\text{U}}^{91+}$ one-electron quasi-molecule are evaluated with the use of the model operator approach. The QED contributions to the ionization energies in the alkali metals are obtained both by averaging the model operator with the valence electron wave functions and by incorporating the QED operator into the Dirac–Coulomb–Breit Hamiltonian. The two-center calculations of the vacuum-polarization and self-energy contributions to the Lamb shift in the one-electron quasi-molecule are performed for the different values of the internuclear distances (from the chemical distances up to the critical ones), the more simplified evaluation in the monopole approximation is also considered. The results of the calculations are compared with the theoretical predictions obtained previously in the framework of the ab initio approaches.