A Simple Equation of State for Nonspherical and Associating Molecules

A simple semiempirical model is presented that gives an accurate representation of the thermodynamic properties for hydrogen bonding and nonspherical molecules. The model is shown to provide a good representation of available molecular simulation data for hard chains, hard spherocylinders, square-well spheres, Lennard-Jones chains, and dimerizing spheres. The simplicity of the model leads to an equation of state that can be applied easily and generally via corresponding states. The equation of state is cubic for nonassociating fluids and has only three real roots for associating fluids. Analysis of hydrogen-bonding systems shows that specifically accounting for molecular association clearly improves the equation's ability to represent mixture phase equilibrium data.