Molecular dynamics investigation of the intrinsic structure of water-fluid interfaces via the intrinsic sampling method

Capillary wave fluctuations smooth out the structure of fluid interfaces, making difficult the detailed analysis of the interfacial structure. Most computer simulation investigations performed to date have focused on the computation of average density profiles, ignoring the characterization of the intrinsic structure of the interface. Recent theoretical developments have reversed this situation, making possible the detailed investigation of the interfacial intrinsic structure at an unprecedented level of detail. In this article we investigate via molecular dynamics simulations the intrinsic structure of water-alkane (hexane and dodecane) interfaces. The implementation of the recently introduced, intrinsic sampling method to compute the intrinsic surface of water-fluid interfaces is discussed. We provide quantitative molecular information on the structure, corrugation, and stiffness of the liquid surfaces. The intrinsic structure of water at alkane interfaces is shown to be insensitive to the alkane-chain length, and can be very accurately described by the intrinsic structure of the water free surface.