Evidence for an Orientationally Ordered Two-Dimensional Fluid Phase from Molecular-Dynamics Calculations

Results of molecular-dynamics calculations on melting in a two-dimensional (2D) Lennard-Jones system are presented. We find that this system loses its resistance to shear at a temperature T₁ (0. 36). However, long-range "orientational" order persists up to a higher temperature T₂ (0. 57). These observations are compatible with the existence of a liquid-crystal-like phase with sixfold anisotropy separated from both the solid and the isotropic-fluid phase by second-order phase transitions. Such two-stage melting behavior in 2D has been predicted by Halperin and Nelson.