The van der Waals Theory of Capillarity and Computer Simulation

Abstract

Computer experiments are performed on the determination of thermodynamic properties and structural characteristics of the Lennard-Jones fluid in one- and two-phase models to check the basic concepts of the van der Waals theory of capillarity. Calculations are performed using molecular dynamics method. It is shown that, at T* ≥ 1.1, the properties of flat interface can be described, within the limits of computer experiment error, in terms of the van der Waals gradient theory with the density-independent influence parameter κ. The account of density dependence of κ via the second moment of direct correlation function deteriorates the agreement between the theory and the data of computer simulation. The contribution of inhomogeneous system of higher (than (∇ρ)2) terms to the Helmholtz free energy of inhomogeneous system is considered. It is shown that the account of terms proportional to (∇ρ)4 does not lead to the agreement between the theory and the data of computer simulation, whereas the consideration of terms proportional to (∇ρ)6 makes it possible to describe (with a good accuracy) all the properties of flat interface within the temperature range from triple point to the critical one.