ABSTRACT
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 â¼ 3.4 Å and a global minimum at smaller ionic separations r â² 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.
ABSTRACT
The recently developed ab initio many-body theory of positron molecule binding [22J. Hofierka et al., Many-body theory of positron binding to polyatomic molecules, Nature (London) 606, 688 (2022)NATUAS0028-083610.1038/s41586-022-04703-3] is combined with the shifted pseudostates method [A. R. Swann and G. F. Gribakin, Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules using a Gaussian basis, Phys. Rev. A 101, 022702 (2020)PLRAAN2469-992610.1103/PhysRevA.101.022702] to calculate positron scattering and annihilation rates on small molecules, namely H_{2}, N_{2}, and CH_{4}. The important effects of positron-molecule correlations are delineated. The method provides uniformly good results for annihilation rates on all the targets, from the simplest (H_{2}, for which only a sole previous calculation agrees with experiment), to larger targets, where high-quality calculations have not been available.
