Prediction of 1P Rydberg energy levels of beryllium based on calculations with explicitly correlated Gaussians

Benchmark variational calculations are performed for the seven lowest 1s22s np (1P), n = 2…8, states of the beryllium atom. The calculations explicitly include the effect of finite mass of 9Be nucleus and account perturbatively for the mass-velocity, Darwin, and spin-spin relativistic corrections. The wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian functions. Basis sets of up to 12 500 optimized Gaussians are used. The maximum discrepancy between the calculated nonrelativistic and experimental energies of 1s22s np (1P) →1s22s2 (1S) transition is about 12 cm−1. The inclusion of the relativistic corrections reduces the discrepancy to bellow 0.8 cm−1