Lowest 2S Electronic Excitations of the Boron Atom

A theoretical ab initio approach for calculating bound states of small atoms is developed and implemented. The approach is based on finite-nuclear-mass [non-Born-Oppenheimer (non-BO)] nonrelativistic variational calculations performed with all-particle explicitly correlated Gaussian functions and includes the leading relativistic and quantum electrodynamics energy corrections determined using the non-BO wave functions. The approach is applied to determine the total and transition energies for the lowest four S-2 electronic excitations of the boron atom. The transition energies agree with the available experimental values within 0.2-0.3 cm(-1). Previously, such accuracy was achieved for three-and four-electron systems.