Systematics of small parahydrogen clusters in two dimensions

We studied by means of computer simulations the low temperature properties of two-dimensional parahydrogen clusters comprising between N = 7 and 30 molecules. Computed energetics is in quantitative agreement with that reported in the only previous study [M. C. Gordillo and D. M. Ceperley, Phys. Rev. B 65, 174527 (2002)], but a generally stronger superfluid response is obtained here for clusters with more than ten molecules. Moreover, all the clusters, including the smallest one, display a well-defined, clearly identifiable solidlike structure; with only one possible exception, those with fewer than N = 25 molecules are (almost) entirely superfluid at the lowest temperature considered here (i.e., T = 0.25 K), and can thus be regarded as nanoscale "supersolids." The implications of these results on a possible bulk two-dimensional superfluid phase of parahydrogen are discussed.