Energetics and structure of Ps-HPs using a molecular approach

Many atoms and negative ions are able to bind a positron. Their structure consists of an atomic core with an orbiting positron or positronium (Ps). A few systems can also bind two positrons, but much less is known about their internal structure. We examine the family pen-em+ with a proton p, n≤4 electrons, and m≤2 positrons. Using quantum Monte Carlo techniques, we study the energetics and structure of pe4-e2+. We compute its ground-state energy [-1.05910(1) hartree] and its binding energy (0.0079 hartree). We show that to construct a bound variational wave function, despite having a single nucleus, we must adopt a molecular description of this system, using HPs, Ps-, H-, and Ps2 as interacting fragments. The analysis of the electronic and positronic probability distributions reveals that at zero order, the internal structure of this system consists of a Ps- interacting with the HPs core. Based on these results, we speculate about the existence of similar systems containing three positrons.