Density functional theory: Modelling of surface tensions for molecular fluids

Abstract

AbstractBoth density profiles, surface tension and the corresponding phase equilibria are governed by the same intermolecular forces. Thus an appropriate theoretical model should be able to describe both interfacial and bulk properties by the same interaction potential. The Local Density Approximation to the Density Functional Theory is applied to the modelling of surface tension and saturated liquid densities of nonpolar molecular fluids. To take into account the nonspherical molecular shape a site‐site Lennard‐Jones interaction potential is used. The reference system is described by a hard convex body equation of state whereas the attractive contributions to the free energy were obtained from a mean‐field approximation. For a series of diatomics structures (O2, N2, CO, Cl2, ethane, ethylene) and convex core geometries (n‐alkanes, benzene, CCl4) potential parameters were estimated using surface tensions and liquid densities. The geometrical parameters for the n‐alkanes could be extrapolated up to n‐octane. A functional dependence of the potential parameters on the chain length and geometry of the molecule is discussed.