Computer simulation of quantum melting in hydrogen clusters

We introduce a new criterion, based on multiple dynamical correlations calculated within reptation quantum Monte Carlo to discriminate between a melting versus freezing behavior in quantum clusters. This criterion is applied to small clusters of para-hydrogen molecules (both pristine and doped with a CO chromophore) for cluster sizes of around twelve molecules. This is a magic size at which para-hydrogen clusters display an icohedral structure and a large stability. Despite the similar geometric structure of CO@pH(2))(12) and (pH(2))(13), the first system has a rigid crystalline, behavior the second behaves more like a superfluid (or, possibly a supersolid).