UB association bias algorithm applied to the simulation of hydrogen fluoride

Abstract

We present a method for accelerating convergence of Monte Carlo (MC) simulations of associating fluids and describe its application to a model for hydrogen fluoride. The new bias scheme preferentially attempts MC trials that lead to unbonding–bonding (UB) transitions of the associating molecules. We apply the algorithm to evaluate properties of the Cournoyer–Jorgensen model of hydrogen fluoride (HF). Superheated vapor properties are calculated from NPT MC simulations over the temperature range of 295.25–318.75 K. Heat capacities and vapor densities are shown. The Gibbs Ensemble technique with UB biasing was used to calculate vapor–liquid coexistence properties over temperatures ranging from 250 to 350 K. Heat of vaporization, coexistence densities and vapor pressures are reported. Simulations performed with no biasing disagree significantly from the UB algorithm data and the new simulations differ also from MC data taken using another biasing algorithm previously developed in our group. The new results coincide better with experimental data taken from the literature for the same state conditions.