A DIRECT METHOD FOR DETERMINATION OF CHEMICAL-POTENTIAL WITH MOLECULAR-DYNAMICS SIMULATIONS .2. MIXTURES

A new direct method for the determination of chemical potentials from molecular dynamics simulations is proposed. This paper focuses on deve lopment and testing of the method for binary mixtures of Lennard-Jones fluids. The proposed method uses a semipermeable membrane to mimic an osmotic experiment. The excess chemical potential is obtained directl y from the osmotic pressure that develops across the membrane and the equilibrium mole fraction of the component to which the membrane is pe rmeable. The method is capable of accurate determination of the chemic al potential of either component in the mole fraction range 0.2 < x(i) < 1. The Gibbs-Duhem equation can be used in conjunction with the ind ividual component simulations in the above range to obtain the chemica l potentials and the excess free energy over the entire composition ra nge. The new method was tested for Lennard-Jones mixtures of various s ize and energy ratios by direct comparison of chemical potentials and excess free energies obtained from the osmotic simulations with values available in the literature which were obtained using other methods.