Thermal dissociation of dipositronium: path integral Monte Carlo approach

TL;DR

This study uses path integral Monte Carlo simulations to investigate the thermal stability of dipositronium molecules, revealing a sharp dissociation transition around 1000 K and highlighting the complex quantum interactions involved.

Contribution

It provides the first detailed simulation-based analysis of Ps$_2$ thermal dissociation, emphasizing the role of quantum correlations and entropy in its stability.

Findings

Ps$_2$ dissociates above ~1000 K at low densities

Stable Ps$_2$ molecules observed below 1000 K

Strong quantum correlations affect interatomic interactions

Abstract

Path integral Monte Carlo simulation of the dipositronium "molecule" Ps$_2$ reveals its surprising thermal instability. Although, the binding energy is $\sim 0.4$ eV, due to the strong temperature dependence of its free energy Ps$_2$ dissociates, or does not form, above $\sim 1000$ K, except for high densities where a small fraction of molecules are in equilibrium with Ps atoms. This prediction is consistent with the recently reported first observation of stable Ps$_2$ molecules by Cassidy & Mills Jr., Nature {\bf 449}, 195 (07), and Phys.Rev.Lett. {\bf 100}, 013401 (08); at temperatures below 1000 K. The relatively sharp transition from molecular to atomic equilibrium, that we find, remains to be experimentally verified. To shed light on the origin of the large entropy factor in free energy we analyze the nature of interatomic interactions of these strongly correlated quantum particles. The conventional diatomic potential curve is given by the van der Waals interaction at large distances, but due to the correlations and high delocalization of constituent particles the concept of potential curve becomes ambiguous at short atomic distances.