Determination of Excess Gibbs Free Energy from Computer Simulation: Multiple-Parameter Charging Approach

Abstract

We devise a general procedure for determining the excess Gibbs free energy from molecular-scale computer simulations of binary mixtures. The method is based upon Kirkwood's coupling-parameter interpretation of the chemical potential. We show that, by a suitable choice of integration path, coupling involving any number of parameters can be represented by a single independent parameter. Thus for (rigid-molecule) solutions made nonideal by differences among several potential parameters, the determination of the excess free energy generally requires little more effort than if all the differences reside in one potential parameter. The development here is an extension of the recent revision of the coupling-parameter approach that avoids the need for the pure component free energies in obtaining the excess free energy of the mixture.