Molecular-based equation of state for TIP4P water

Using a theoretically justified decomposition of realistic intermolecular pair potentials into a short-range reference model and a perturbation part, one obtains the Helmholtz free energy in a form made up of several terms, each originating from a different type of interaction. Using a primitive model to estimate the properties of the short-range reference in an analytic form, this decomposition has been used to derive an equation of state of TIP4P water using the vapor-liquid equilibrium data to adjust its parameters. It is shown that the equation reproduces the thermodynamic properties of TIP4P water reasonably well including the temperature density maximum.