Accurate Kirkwood-Buff integrals from molecular simulations

A method is proposed for obtaining thermodynamic properties via Kirkwood-Buff (KB) integrals from molecular simulations. In order to ensure that the KB integration converges, the pair distribution function is extrapolated to large distances using the extension method of Verlet, which enforces a theoretical limiting behaviour on the corresponding direct correlation function. The method is evaluated for the pure Lennard-Jones and Stockmayer fluids. The results are verified by comparing pure fluid isothermal compressibilities obtained from the KB integrals with values from derivatives of equations of state fitted to simulation results. Good agreement is achieved for both fluids at densities larger than 1.5 times the critical density.