MELTING IN 2 DIMENSIONS

New Monte Carlo computer simulations of hard-disk systems containing 16 384 particles show that a first-order phase transition occurs at a higher pressure and is more weakly first order than has long been believed. The results that led to the description of the transition as strongly first order have been reproduced in simulations of 1024 disks. A free-energy model developed using the double-histogram method of Ferrenberg and Swendsen has been used to correlate the N-A Monte Carlo data obtained at different densities. This analysis shows a tie line only half as long as the classical one and a very large compressibility for the ordered phase near the transition. Further investigation will be necessary to determine the nature of that ordered phase.