A DIRECT METHOD FOR DETERMINATION OF CHEMICAL-POTENTIAL FROM OSMOTIC MOLECULAR-DYNAMICS SIMULATIONS

A new direct method for determination of chemical potentials from mole cular dynamics simulations is proposed. This paper focuses on developm ent and testing of the method for pure, Lennard-Jones fluids. The prop osed method uses a semipermeable membrane to mimic an osmotic experime nt. With only a few particles designated as those to which the membran e is permeable, the chemical potential relative to that of an ideal ga s can be determined for a fluid at virtually any realistic temperature and density, and only the equilibrium mole fraction of the permeable particles in the ''mixture'' side of the cell is required. The chemica l potentials obtained using the new osmotic method agree well with tho se obtained from the Lennard-Jones equation of state and those obtaine d from Widom's method. The new method has the main advantage over trad itional methods of being extendable to complex molecules because no pa rticle insertions are required.