Microscopic theory of liquid interfaces in molecular systems

A statistical-mechanical theory of inhomogeneous polyatomic fluids is proposed. It enables microscopic description of liquid interfaces in molecular systems with both non-polar and polar species. The method introduces a site-site generalization of the Lovett-Mow-Buff-Wertheim integro-differential equation for the one-particle density distributions to polyatomic fluids. It uses the inhomogeneous site-site direct correlation functions of molecular fluid consistently constructed by nonlinear interpolation between the homogeneous ones. The site-site correlations of the coexisting bulk phases are obtained from the reference interaction site model (RISM) integral equation with the closure approximation proposed by Kovalenko and Hirata. The theory is applied to the planar liquid-vapor as well as liquid-liquid interfaces of n-hexane and methanol in ambient conditions.