The role of attractive interactions in the dynamics of molecules in liquids

The friction kernel (or memory function) $\gamma(t)$ characterizing single-molecule dynamics in strongly bound liquids exhibits two distinct relaxations with the longer time-scale relaxation associated with attractive intermolecular forces. This observation identifies differing roles of repulsive and attractive interaction in the motions of molecules in equilibrium liquids, and thus provides a basis for a renewed investigation of a van der Waals picture of the transport properties of liquids. This conclusion is supported by extracting $\gamma(t)$ from molecular dynamics simulation data for four common molecular liquids.