Phase diagram of D2 adsorbed on graphene and graphite

The phase diagram of o-D-2 adsorbed on top of both graphene and graphite was calculated for T = 0 K using the diffusion Monte Carlo technique. Both diagrams were found to be virtually identical, except for the energy offset due to the presence of additional graphene sheets in graphite. The ground state of D-2 on graphene and graphite was a root 3 x root 3 commensurate structure that upon a pressure increase was transformed into a so-called gamma phase, characterized by an oblique unit cell rotated a given angle with respect to the axis of the upper graphene sheet. At even higher densities, a triangular incommensurate structure similar to the one in the H-2 case is found. A delta commensurate phase at 0.0789 angstrom(-2) can barely be distinguished from the gamma incommensurate solid at this density, but an epsilon commensurate structure at 0.0835 angstrom(-2) is more stable than its gamma counterpart. Between the root 3 x root 3 structure and the gamma solid, a striped domain wall alpha phase was found to be more stable than a mixture of both.