S 2 Rydberg spectrum of the boron atom

Benchmark variational calculations of the lowest ten Rydberg S2 states of two stable isotopes of the boron atom (B10 and B11) are reported. The nonrelativistic wave functions of this five-electron system are expanded in terms of 16 000 all-particle explicitly correlated Gaussians (ECGs). The ECG nonlinear exponential parameters are extensively optimized using a procedure that employs the analytic gradient of the energy with respect to these parameters. A finite nuclear mass value is used in the calculations and the motion of the nucleus is explicitly represented in the nonrelativistic Hamiltonian. The leading relativistic corrections to the energy levels are computed in the framework of the perturbation theory. The lowest-order quantum electrodynamics corrections are also estimated. The results obtained for the energy levels enable determination of interstate transition frequencies with accuracy that approaches the available experimental spectroscopic data.