Two Protons, Two Positrons, and Four Electrons: Covalent Bond with van der Waals Characteristics

TL;DR

This study uses quantum Monte Carlo calculations to analyze the bonding nature in positronium hydride dimers, revealing a covalent-like positronic bond with van der Waals strength, indicating delocalized proto-bonds may be common in quantum systems.

Contribution

It demonstrates that positronic bonding involves quantum correlations resembling covalent bonds, expanding understanding of bonding mechanisms in matter-antimatter systems.

Findings

Positrons occupy a delocalized molecular orbital around hydrogen anions.

The positronic bond has covalent-like characteristics but van der Waals strength.

Delocalized proto-bonds may be a general property of quantum systems.

Abstract

Classifying interactions is key in the physical sciences, and bonding mechanisms in matter-antimatter systems remain particularly enigmatic. Here we focus on a paradigmatic example of positronium hydride (PsH) dimer composed of two protons, two positrons, and four electrons, whose bonding nature has been previously described as either ionic, covalent, or van der Waals-like. Accurate quantum Monte Carlo calculations show that the two positrons occupy a delocalized molecular orbital that envelopes the two hydrogen anions and responds as a collective dipole to an applied electric field. This positronic bonding stems from quantum correlations that resemble a single covalent bond formed between negatively charged pseudo-nuclei, but with a bond strength commensurate with the traditional van der Waals interaction. Our findings suggest that the ability to form delocalized proto-bonds is a more general property of quantum systems, and could be present in a broader class of particles, antiparticles, and quasi-particles interacting with matter.