Physically based equation of state for Mie ?-6 fluids

We develop a physically based equation of state that describes Mie ?-6 fluids with an accuracy comparable to that of state-of-the-art empirical models. The equation of state is developed within the framework of the uv-theory [T. van Westen and J. Gross, J. Chem. Phys. 155, 244501 (2021)], which is modified by incorporating the third virial coefficient B-3 in the low-density description of the model. The new model interpolates between a first-order Weeks-Chandler-Andersen (WCA) perturbation theory at high densities and a modified first-order WCA theory that recovers the virial expansion up to B-3 at low densities. A new algebraic equation for the third virial coefficient of Mie ?-6 fluids is developed-other inputs are taken from previous work. Predicted thermodynamic properties and phase equilibria are compared to a comprehensive database of molecular simulation results from the literature, including Mie fluids of repulsive exponents 9 = ? = 48. The new equation of state is applicable to states with densities up to ?*(T*) ? 1.1+0.12vT* and temperatures T* > 0.3. For the Lennard-Jones fluid (? = 12), the performance of the model is comparable to that of the best empirical equations of state available. As compared to empirical models, the physical basis of the new model provides several advantages, however: (1) the new model is applicable to Mie fluids of repulsive exponents 9 = ? = 48 instead of only ? = 12, (2) the model leads to a better description of the meta-stable and unstable region (which is important for describing interfacial properties by classical density functional theory), and (3) being a first-order perturbation theory, the new model (potentially) allows an easier and more rigorous extension to non-spherical (chain) fluids and mixtures.

Automated summary

We developed a physically based equation of state for Mie-6 fluids that has a comparable accuracy to state-of-the-art empirical models. The equation of state combines uv-theory with the third virial coefficient to provide an accurate description of high and low density regimes. The new model has several advantages over empirical models, including applicability to a wider range of repulsive exponents and better description of meta-stable and unstable regions.