Eight-valence electron configuration-interaction many-body perturbation theory calculations of noble-gas atoms

Excited states of noble-gas atoms present certain difficulties to configuration-interaction many-body perturbation theory (CI-MBPT). One specific problem is that in formalism of particle-hole CI-MBPT, the perturbation theory for hole states does not converge well. One solution was proposed to use either all-order methods [1] or to modify MBPT denominators [2]. In the current work, on example of Ar, we find that this problem can be solved by treating 3s and 3p electrons as valence electrons (8 total), and by including the residual interactions with 1s, 2s, 2p core electrons via MBPT. The configuration space grows very quickly with the number of allowable excitations, so we impose certain constrains on them, for example by excluding triplet excitations, to have manageable CI space. We find that with our approach we can obtain energies, g factors, and matrix elements in reasonable agreement with experiments and other calculations.
1. E. N. Avgoustoglou and D. R. Beck, Phys. Rev. A 57, 4286 (1998).
2. I. M. Savukov, W. R. Johnson, and H. G. Berry, Phys. Rev. A 66, 052501 (2002).