A thermodynamic scaling Monte Carlo method to determine the unlike pair interaction parameter

For computer simulations on fluid phase equilibrium calculations, an important issue is to determine the unlike pair interaction parameter between unlike components, which is at present determined by a trial-and-test method or by laborous iterative calculations. In this work, basing on the thermodynamic scaling method put forward and developed by Graham, Valleau and Kiyohara etc, we propose a new method to calculate the fluid phase equilibria for a range of unlike pair interaction parameters in a single simulation run, which makes the determination of unlike parameter much easily. In this work, we also present a method to optimize the weight in thermodynamics scaling Monte Carlo methods. The method, which is based on the perturbation theory, requires only a single simulation run on a reference state. Our simulation results indicate that the method converges quickly and improves greatly the calculation accuracy.