Assessment of the accuracy the experimental energies of the 1P(o) 1s(2)2s6p and 1s(2)2s7p states of 9Be based on variational calculations with explicitly correlated Gaussians.

Benchmark variational calculations are performed for the six lowest states of the (1)P(o) 1s(2)2snp state series of the (9)Be atom. The wave functions of the states are expanded in terms of all-particle, explicitly correlated Gaussian basis functions and the effect of the finite nuclear mass is directly included in the calculations. The exponential parameters of the Gaussians are variationally optimized using the analytical energy gradient determined with respect to those parameters. Besides providing reference non-relativistic energies for the considered states, the calculations also allow to assess the accuracy of the experimental energies of the (1)P(o) 1s(2)2s6p and 1s(2)2s7p states and suggest their refinement.