Ground and excited S1 states of the beryllium atom

Abstract

Benchmark calculations of the total and transition energies of the four lowest S-1 states of the beryllium atom are performed. The computational approach is based on variational calculations with finite mass of the nucleus. All-particle explicitly correlated Gaussian (ECG) functions are used to expand the total non-Born-Oppenheimer nonrelativistic wave functions and the ECG exponential parameters are optimized using the standard variational method. The leading relativistic and quantum electrodynamics energy corrections are calculated using the first-order perturbation theory. A comparison of the experimental transition frequencies with the ones calculated in this work shows excellent agreement. The deviations of 0.02-0.09 cm(-1) are well within the estimated error limits for the experimental values.