Excess free energy mixing rules for cubic equations of state

There is a rapidly growing literature exploring techniques for implanting specified excess Gibbs free energy behavior into the cubic equations of state through the mixing rules. The Huron and Vidal proposal [1] has been augmented by a number of ideas that employ a low-pressure or zero-pressure standard state, thereby opening the possibility of using directly the group contribution activity coefficient models or specific correlations of low pressure data. Several lines of research are leading toward group contribution models that can include the super-critical gases. These ideas are discussed in the present manuscript.