Tests of a generalized Barker-Henderson perturbation theory for the phase coexistence diagram of an anisotropic potential

The Barker-Henderson perturbation theory is used frequently to compute fluid-fluid and solid-fluid phase coexistence diagrams (PCD). A generalization of this theory for anisotropic pair potentials has been suggested recently (J. Chem. Phys. 129, 085102 (2008)). We test the accuracy of its predictions, through comparison with the results of high statistics Gibbs Ensemble Monte Carlo simulations, for a minimal model that we introduce for anisotropic pair potential without fore-aft symmetry. Agreement is found to be less close than in previous applications of this generalized Barker-Henderson theory. We also show that our minimal model captures some essential aspects of the experimental PCDs of many simple fluids and some globular proteins. In particular the flatness of the scaled PCD around the critical point can be enhanced by increasing the value of the anisotropy parameter of our model. Quantitative predictions regarding this are compared with experimental data for lysozyme and gamma IIIa-crystallin.