GIBBS-ENSEMBLE MOLECULAR-DYNAMICS - LIQUID-GAS EQUILIBRIA FOR LENNARD-JONES SPHERES AND N-HEXANE

We present a novel method to simulate phase equilibria in atomic and m olecular systems. The method is a Molecular Dynamics version of the Gi bbs-Ensemble Monte Carlo technique, which has been developed some year s ago for the direct simulation of phase equilibria in fluid systems. The idea is to have two separate simulation boxes, which can exchange particles (or molecules) in a thermodynamically consistent fashion. He re we present the derivation of the generalized equations of motion an d discuss the relation of the resulting trajectory averages to the rel evant ensemble. We test this Gibbs-Ensemble Molecular Dynamics algorit hm by applying it to an atomic and a molecular system, i.e. to the liq uid-gas coexistence in a Lennard-Jones fluid and in n-hexane. In both cases our results are in good accord with previous mean field and Gibb s-Ensemble Monte Carlo results as well as with the experimental data i n the case of hexane. We also show that our Gibbs-Ensemble Molecular D ynamics algorithm like other Molecular Dynamics techniques can be used to study the dynamics of the system. Self-diffusion coefficients calc ulated with this method are in agreement with the result of convention al constant temperature Molecular Dynamics.