Computer Simulation Study of Nanoscale Size Parahydrogen Clusters

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 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.

Microscopic Pair Potentials and the Physical Properties of the Condensed Phases of Parahydrogen

“…For completeness, we also report results of some calculations in which the Buck and the ab initio potential by Diep and Johnson [26] were utilized. The purpose of this project is to determine whether recent ab initio potentials (and specifically the P) may represent a better choice than the SG, as a general-purpose potential to study condensed phases of p-H 2 in different settings, including droplets [42][43][44], as well as in confinement [45,46].…”

Evidence for melting of HD and D2 clusters in solid neon below 1 K

“…The freezing temperature is proportional to the cluster size and may approach zero for very small clusters [6]. The aggregates of a larger size containing ≃10 4 molecules may still remain liquid at temperature as low as ≃1 K if prepared in the transient metastable state [6], even though no superfluidity is expected for such clusters in a steady equilibrium state [4], [7].…”