Stability and bonding nature of positronic lithium molecular dianion

Abstract

We studied the stability of a system consisting of a positron (e+) and two lithium anions, [Li−; e+; Li−], using first-principles quantum Monte Carlo calculations combined with the multi-component molecular orbital method. While diatomic lithium molecular dianions Li22− are unstable, we found that its positronic complex can form a bound state with respect to the lowest energy decay into the dissociation channel Li2− and a positronium (Ps). The [Li−; e+; Li−] system has the minimum energy at the internuclear distance of ∼3 Å, which is close to the equilibrium internuclear distance of Li2−. At the minimum energy structure both an excess electron and a positron are delocalized as orbiting around the Li2− molecular anion core. A dominant feature of such a positron bonding structure is described as the Ps fraction bound to Li2−, unlike the covalent positron bonding scheme for the electronically isovalent [H−; e+; H−] complex.