Inherent structures and two-stage melting in two dimensions

A large-scale study of the ''inherent structures'' (IS) associated with equilibrium two-dimensional Lennard-Jones systems is presented. The results validate, for simple 2D fluids, an essential premise of inherent-structures theory: there are consistent, qualitative differences between the IS associated with distinct equilibrium phases. The hexatic IS show free dislocations plus some nonpercolating grain boundaries. The liquid IS always contain percolating grain boundaries, but no evidence of free disclinations. Our results are consistent with the dislocation-unbinding scenario for the hexatic phase, but leave open the question of the microscopic melting mechanism leading to the isotropic liquid.