Molecular Dynamics Exploration of Properties in the Liquid-Vapor Interfacial Region Available to Purchase

Molecular dynamics (MD) simulations of liquid-vapor interfaces were performed to determine mean property variations and property fluctuations in the liquid-vapor interfacial region at various reduced temperatures. The interfacial region typically has a thickness on the order of a few nanometers for systems of practical interest. The system’s initial conditions were specified as a bulk liquid region sandwiched between two bulk vapor regions. Simulations were run using a Lennard-Jones 6-12 potential function between the atoms with appropriate parameters for Argon atoms. As the simulation was performed, interfacial region property data was collected over time. The resulting property data are shown to establish trends similar to those indicated by theoretical and experimental results reported elsewhere. The peak fluctuations of mass density and free energy density were determined to be approximately equal in magnitude when normalized with the difference in their respective bulk values at a given temperature. These fluctuations were found to increase rapidly with temperature. The fluctuations in the interfacial thickness and interfacial position follow a functional dependence on temperature similar to that exhibited by the mean value of interfacial thickness. In addition to exploring fluctuations in the interfacial region, two new methods were developed to determine interfacial tension through methods involving integration of excess free energy density across the interfacial region. These techniques were shown to yield mean results similar to theoretical predictions and those using conventional techniques. In addition, the time required for computation using the new techniques is significantly reduced due to less computational time per step and fewer required steps for convergence to a mean value.