Optimisation of multiple time-step hybrid Monte Carlo Wang-Landau simulations in the isobaric-isothermal ensemble for the determination of phase equilibria

We discuss the optimisation as well as the convergence of a recently developed molecular simulation method using a Wang-Landau sampling scheme, combined with multiple time-step hybrid Monte Carlo (MC) simulations in the isothermal-isobaric ensemble, to determine vapour-liquid equilibria. This method has the advantage of being simple to use, as only a single simulation run at a given temperature directly gives the coexistence properties, and of being transferable to any kind of fluid, since the method is readily applicable to any molecular architecture. We apply this method to two branched alkanes, isopentane and isobutane, and discuss how we optimise the various simulation parameters. The vapour-liquid coexistence curve as well as the critical point obtained in this work are in excellent agreement with those found experimentally and in previous work using a combination of the Gibbs ensemble MC method with the configurational bias technique.