engleski

He-4 clusters adsorbed on graphene

We report the results of the study of $^4$He$_N$ clusters adsorbed on one and both sides of a graphene sheet. Interactions of $^4$He clusters with graphene are modelled using a smooth helium- carbon potential that depends only on the distance to the graphene sheet, and a potential constructed as a sum of individual helium-carbon interactions where two choices for this He-C interaction are tested. That way, we assess the effect of corrugation on the binding properties of helium clusters. Furthermore we study the influence that the graphene-mediated McLachlan dispersion energy has on the He-He interaction. The McLachlan interaction weakens the attraction between helium atoms, which has a significant effect on the binding energy and shape of adsorbed $^4$He clusters. All the calculations have been performed using quantum Monte Carlo methods. At zero temperature the ground-state properties of $^4$He$_N$ for 2$\le N\le$40 have been determined using variational and diffusion Monte Carlo calculations, and in addition path integral Monte Carlo simulations at finite temperature have been performed for some selected cluster sizes. We find that clusters adsorbed on both sides of graphene are bound but according to the He-He pair distribution function across the graphene sheet pair correlations are negligible.

graphene ; He-4 clusters ; Monte Carlo methods

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