Thermal and structural properties of the liquid-vapor interface in dipolar fluids

Based on a recently developed density-functional theory for inhomogeneous molecular fluids [P. Frodl and S. Dietrich, Phys. Rev. A 45, 7330 (1992)], we investigate the profiles of the number density and of the orientational order at the liquid-vapor interface of a Stockmayer fluid as well as the corresponding surface tension. We systematically analyze the dependencies of these quantities on the temperature and on the strength of the permanent dipole moment of the molecules. This reveals power laws and scaling behavior. Our approach, which is reliable even for large dipole moments, allows us to determine separately those contributions to the surface tension which are due to the orientational degrees of freedom.