Many-body theory calculations of positronic-bonded molecular dianions

The energetic stability of positron-dianion systems [A^-; e⁺; A^-] is studied via many-body theory, where A^- includes H^-, F^-, Cl^-, and the molecular anions (CN)^- and (NCO)^-. Specifically, the energy of the system as a function of ionic separation is determined by solving the Dyson equation for the positron in the field of the two anions using a positron-anion self-energy as constructed in Hofierka et al. [Nature 606, 688 (2022)] that accounts for correlations, including polarization, screening, and virtual-positronium formation. Calculations are performed for a positron interacting with H²₂^-, F²₂^-, and Cl²₂^- and are found to be in good agreement with previous theory. In particular, we confirm the presence of two minima in the potential energy of the [H^-; e⁺; H^-] system with respect to ionic separation: a positronically bonded [H^-; e⁺; H^-] local minimum at ionic separations r ∼ 3.4 Å and a global minimum at smaller ionic separations r ≲ 1.6 Å that gives overall instability of the system with respect to dissociation into a H₂ molecule and a positronium negative ion, Ps^-. The first predictions are made for positronic bonding in dianions consisting of molecular anionic fragments, specifically for (CN)²₂^- and (NCO)²₂^-. In all cases, we find that the molecules formed by the creation of a positronic bond are stable relative to dissociation into A^- and e⁺A^- (positron bound to a single anion), with bond energies on the order of 1 eV and bond lengths on the order of several ångstroms.