Configuration-interaction calculations of positron binding to group-II elements

Abstract

The configuration-interaction (CI) method is applied to the study of positronic magnesium ${(e}^{+}\mathrm{Mg}),$ positronic calcium ${(e}^{+}\mathrm{Ca}),$ and positronic strontium ${(e}^{+}\mathrm{Sr}).$ The CI expansion was seen to converge slowly with respect to ${L}_{\mathrm{max}},$ the maximum angular momentum of any orbital used to construct the CI basis. Despite doing explicit calculations with ${L}_{\mathrm{max}}=10,$ extrapolation corrections to the binding energies for the ${L}_{\mathrm{max}}\ensuremath{\rightarrow}\ensuremath{\infty}$ limit were substantial in the case of ${e}^{+}\mathrm{Ca}$ (25%) and ${e}^{+}\mathrm{Sr}$ (50%). The extrapolated binding energies were 0.0162 hartree for ${e}^{+}\mathrm{M}\mathrm{g},$ 0.0165 hartree for ${e}^{+}\mathrm{Ca},$ and 0.0101 hartree for ${e}^{+}\mathrm{Sr}.$ The static-dipole polarizabilities for the neutral parent atoms were computed as a by-product, giving ${71.7a}_{0}^{3},$ ${162a}_{0}^{3},$ and ${204a}_{0}^{3}$ for Mg, Ca, and Sr, respectively.