Hylleraas-configuration-interaction nonrelativistic energies for the ¹S ground states of the beryllium isoelectronic sequence.

In a previous work, Sims and Hagstrom ["Hylleraas-configuration-interaction study of the 1 (1)S ground state of neutral beryllium," Phys. Rev. A 83, 032518 (2011)] reported Hylleraas-configuration-interaction (Hy-CI) method variational calculations for the (1)S ground state of neutral beryllium with an estimated accuracy of a tenth of a microhartree. In this work, the calculations have been extended to higher accuracy and, by simple scaling of the orbital exponents, to the entire Be 2 (1)S isoelectronic sequence. The best nonrelativistic energies for Be, B(+), and C(++) obtained are -14.6673 5649 269, -24.3488 8446 36, and -36.5348 5236 25 hartree, respectively. Except for Be, all computed nonrelativistic energies are superior to the known reference energies for these states.