Size dependent solvatation of p-H2 in 4He nanodroplets: A quantum Monte Carlo analysis

Variable-size He-4(N) clusters doped with a single p-H-2 molecule are studied here using variational and diffusion Monte Carlo calculations that show the highly quantum nature of the dopant and the solvent. Energetic and structural features extracted from our analysis reveal that the p-H-2 molecule behaves as a gentle perturber: The He droplets remain essentially liquidlike, with no evident structural change with respect to the pure ones. The p-H-2 dopant represents a kind of "competitor" for helium in the smaller droplets because it can replace the solvent adatoms; it also remains immersed in the cluster as N increases although located off-center within the droplet, while, finally, getting fully solvated in the larger droplets. The calculations are carried out up to N=100 as the largest number of solvent He-4 atoms and clearly show no evidence of either shell structuring or of "magic" numbers in the size of the smaller droplets.