Many-body perturbation theory applied to eight states of BH

The energy of the ground and seven excited states of BH was calculated using many-body perturbation theory (MBPT). The usual Goldstone diagrammatic expansion was applied to the ground state, and the Brandow formulation of degenerate MBPT was applied to the excited states. Corrections to third order (inclusive) were calculated. The resulting vertical excitation energies agree with experiment to better than 3% (about 0.1 eV). Transition moments are also reported.