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

Recent lattice model calculations have suggested that a full-layered crysta l surface may undergo, under canonical (particle-conserving) conditions, a preroughening-driven two-dimensional phase separation into two disordered f lat regions, of opposite order parameter. We have carried out extensive cla ssical molecular dynamics (MD) simulations of the Lennard-Jones fcc(lll) su rface, to check whether these predictions are relevant or not for a realist ic continuous system. Very long simulation times, a grid of temperatures fr om 2/3 T-m to T-m, and unusually large system sizes are employed to ensure full equilibrium and good statistics. By examining layer-by-layer occupanci es, height fluctuations, sublattice order parameter and X-ray structure fac tors, we find a clear anomaly at similar to 0.83T(m). The anomaly is distin ct from roughening (whose incipiency is also detected at similar to 0.94T(m )), and is seen to be consistent with the preroughening plus phase separati on scenario. (C) 2000 Elsevier Science B.V. All rights reserved.