Phase diagram of H2 adsorbed on graphene

TL;DR

This paper uses diffusion Monte Carlo simulations to map the phase diagram of the first layer of H2 on graphene, revealing a sequence of solid phases similar to helium, including commensurate, incommensurate, and striped structures.

Contribution

It provides the first detailed quantum Monte Carlo study of H2 adsorption on graphene, identifying the ground state and phase transitions of the first adsorbed layer.

Findings

Ground state is a $ imes $ commensurate structure.

Transition to an incommensurate triangular solid with increased pressure.

Existence of an intermediate striped phase.

Abstract

The phase diagram of the first layer of H$_2$ adsorbed on top of a single graphene sheet has been calculated by means of a series of diffusion Monte Carlo (DMC) simulations. We have found that, as in the case of $^4$He, the ground state of molecular hydrogen is a $\sqrt3 \times \sqrt3$ commensurate structure, followed, upon a pressure increase, by an incommensurate triangular solid. A striped phase of intermediate density was also considered, and found lying on top of the equilibrium curve separating both commensurate and incommensurate solids.