Computer simulation study of nanoscale size parahydrogen clusters

TL;DR

This study uses computer simulations to explore the structural and quantum properties of large parahydrogen clusters at ultra-low temperatures, revealing potential supersolid and superfluid behaviors.

Contribution

It provides the first detailed simulation analysis of nanoscale parahydrogen clusters, highlighting quantum effects and possible supersolid phases.

Findings

Structural similarity to solid bulk parahydrogen

Presence of a supersolid core and superfluid shell

Quantum signatures in momentum distribution

Abstract

We present results of computer simulations of a parahydrogen cluster of a thousand molecules, corresponding to approximately 4 nm in diameter, at temperatures between 1 K and 10 K. Examination of structural properties suggests that the local environment experienced by molecules is very similar to that in solid bulk parahydrogen, especially near the center of the cluster, where crystallization originates. Albeit strongly suppressed compared to helium, quantum-mechanical exchanges are not entirely negligible at the lowest temperature, resulting in a small but significant molecular mobility enhancement with respect to the bulk crystalline phase. Although the overall superfluid response at the lowest temperature is only a few percents, there is evidence of a surprising "supersolid" core, as well as of a superfluid outer shell. Much like in fluid parahydrogen at the melting temperature, quantum-mechanical signatures can be detected in the momentum distribution.