Gaussian core model in two dimensions. II. Solid and fluid phase topological distribution functions

Local structure in the two-dimensional Gaussian core model at p* = 3/2 has been anayzed through the topology of nearest-neighbor polygons. Disorder is revealed by the presence of nonhexagonal polygons (disclinations). Near the melting point most disclination polygons have either five or seven sides and these are present in nearly equal concentrations. The concentrations increase by an order of magnitude upon melting the solid. Within the melting range phase coexistence is revealed by inhomogeneous distribution of disclinations. Pair correlation functions have been calculated for particles classified by polygon character; they show asymmetry with respect to disclination type. The first-order melting process can be described as condensation of a dilute gas of small disclination aggregates (solid phase) into a dense medium of disclinations (fluid phase).