Our paper entitled Choice of reference, influence of non-additivity, and present challenges in thermodynamic perturbation theory for mixtures has just been published in the Journal of Chemical Physics.
In the article, we discuss how thermodynamic perturbation theory should be extended to fluid mixtures, and how different formulations and references will result in different accuracies. All formulations examined in the paper display challenges for Lennard-Jones mixtures with significantly different particle sizes (sigma) or significantly different well depths of their potentials (epsilon). We found that an inaccurate representation of higher order perturbation terms was the reason for this, giving a large overprediction of the pressures in the critical region. This overprediction presently causes problems in the prediction of the thermodynamic properties of fluids such as helium-neon mixtures. We are currently working to improve the theory and overcome these challenges.
The work in the paper has been done in collaboration with Morten Hammer, Ailo Aasen and Åsmund Ervik from SINTEF Energy Research.