Simulation study of the angular dependence of spatial correlation functions in liquids using smoothing filters

Computer simulation results for the angular dependence of spatial correlation functions in liquids are given. The results were obtained using smoothing filters applied to the molecular trajectories of liquids. The purpose of this procedure is to enhance the local structure by attenuating thermal vibrations, and to study low frequency motions. New spatial correlation functions for positions and velocities are measured. These depend not only on distance but also on the angle between the distance vector and the velocity of the reference particle. The results suggest that cooperative self-diffusion is mainly a longitudinal process. An alternative recursive filter is introduced so that the smoothing procedure can be obtained on-line, while the simulation is proceeding. Possible applications include molecular dynamics simulations of solid-liquid interfaces and real-time measurements of local geometry.