Relativistic and QED Corrections for the Beryllium Atom

Complete relativistic and quantum electrodynamics corrections of order α² Ry and α³ Ry are calculated for the ground state of the beryllium atom and its positive ion. A basis set of correlated Gaussian functions is used, with exponents optimized against nonrelativistic binding energies. The results for Bethe logarithms ln⁡k₀(Be)=5.750 34(3) and ln⁡k₀(Be⁺)=5.751 67(3) demonstrate the availability of high precision theoretical predictions for energy levels of the beryllium atom and light ions. Our recommended value of the ionization potential 75 192.514(80)   cm^-1 agrees with equally accurate available experimental values.