Computer simulation of quantum melting in hydrogen clusters

TL;DR

This paper introduces a new quantum Monte Carlo-based criterion to distinguish melting from freezing in small hydrogen clusters, revealing different behaviors in clusters with similar structures but different compositions.

Contribution

The study develops a novel criterion based on multipole dynamical correlations within Reptation Quantum Monte Carlo to analyze quantum melting in hydrogen clusters.

Findings

(pH2)12 is rigid and crystalline.

(pH2)13 exhibits superfluid-like behavior.

The criterion effectively differentiates melting and freezing in quantum clusters.

Abstract

We introduce a new criterion--based on multipole dynamical correlations calculated within Reptation Quantum Monte Carlo--to discriminate between a melting vs. freezing behavior in quantum clusters. This criterion is applied to small clusters of para-hydrogen molecules (both pristine and doped with a CO cromophore), for cluster sizes around 12 molecules. This is a magic size at which para-hydrogen clusters display an icosahedral structure and a large stability. In spite of the similar geometric structure of CO@(pH2)_12 and (pH2)_13, the first system has a rigid, crystalline, behavior, while the second behaves more like a superfluid (or, possibly, a supersolid).