van der Waals-Corrected Ab Initio Study of Water Ice-Graphite Interaction

The interaction between a water-ice bilayer and graphite is investigated by means of standard and van der Waals-corrected density functional theory. The long-range van der Waals attraction proves to be dominant in this context due to the absence of strong chemical bonding between the ice bilayer and graphite. Our calculations suggest that both adsorption of the ice bilayer on graphite and its intercalation between graphene layers are energetically favorable. This second configuration, however, is expected not to be easily realizable due to the elevated energy barrier with respect to the intercalation of a single water molecule. The energy barriers relative to the sliding of the ice bilayer on graphite are also computed. Interestingly, these appear to be two orders of magnitude lower than those relative to graphene-graphene sliding in graphite. This result suggests that the sliding of water on the graphite surface might play a relevant role in determining the well-known lubricating properties of graphite in the presence of humidity.