Relativistic effects in positronic alkali atoms

In order to investigate interactions between a positron/positronium and an atom/ion, we calculate positronic alkali atoms, a loosely bound state of an alkali ion and a positronium, as a three-body system composed of the positron, valence electron and residual ion core within a frozen core approximation. We optimize model potentials to reproduce energy levels and fine structure splittings of alkali atoms. The ion core polarization by a positron is determined more precisely than other previous studies. We found that the relativistic effects amazingly contribute to the binding energy of the positronic alkali atom. We also discuss the rearrangement effect on the relativistic corrections and roles of positronium-ion and atom-positron configurations.