A Molecular Dynamics Study on the Local Structure of Liquid-Vapor Interface of Water and L-J Fluid

Microscopic structures of the liquid-vapor interface are investigated by molecular dynamics simulations. In previous studies, we proposed the local and instantaneous definition of the interface at the molecular level, which can capture the thermal fluctuation of the interface. By using this definition, the layering structure of water molecules at the interface is found, in other words, the structurization phenomena of water at the molecular level are clearly seen as usually found at the liquid-solid interface. In this study, we also investigated the liquid-vapor interface of Lenard-Jones fluid. Well depth of L-J potential parameter was somewhat changed and the effect on the structure was studied. Although the structurization was also found at the L-J fluid as well as water, characteristic of this structure is clearly different from that of water. We consider that the difference is ascribed to the intrinsic structure of liquid and associative trend of molecules. We also discussed the anisotropic character of the molecular diffusion at the interface. The anisotropy of the translational diffusion at the interface of water is stronger than that of the L-J fluid.