Computer Simulation Study of Nanoscale Size Parahydrogen Clusters
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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 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.
KeywordsMolecular hydrogen Superfluidity Quantum clusters Bose–Einstein condensation Quantum Monte Carlo
This work was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC). The author gratefully acknowledges the hospitality of the International Centre for Theoretical Physics, Trieste, where most of this research work was carried out.