Disordered flat phase separation of the Lennard-Jones fcc(111) surface

Abstract Recent lattice model calculations have suggested that a full-layered crystal surface may undergo, under canonical (particle-conserving) conditions, a preroughening-driven two-dimensional phase separation into two disordered flat regions, of opposite order parameter. We have carried out extensive classical molecular dynamics (MD) simulations of the Lennard-Jones fcc(111) surface, to check whether these predictions are relevant or not for a realistic continuous system. Very long simulation times, a grid of temperatures from 2 3 T m to Tm, and unusually large system sizes are employed to ensure full equilibrium and good statistics. By examining layer-by-layer occupancies, height fluctuations, sublattice order parameter and X-ray structure factors, we find a clear anomaly at ∼0.83Tm. The anomaly is distinct from roughening (whose incipiency is also detected at ∼0.94Tm), and is seen to be consistent with the preroughening plus phase separation scenario.