Bulk viscosity of simple liquids

Anomalous intrinsic properties of bulk viscosity at normal states of simple liquids were revealed by molecular dynamics simulations, compared with shear viscosity and thermal conductivity. To this end, we analyzed the partial contributions of the time correlation function in the Green-Kubo formula not only from pair and three-body interactions but also from attractive and repulsive parts. The most distinct feature of bulk viscosity from the other transport properties is sensitivity to the attractive interaction. What is even more interesting is that the effect of attractive interactions is greatly reduced by the introduction of the three-body repulsion, even though the strength of the three-body repulsion itself is very weak and has little effect directly on all the transport coefficients. The mechanism behind this is elucidated in detail through the change in the pair distribution function brought about by the introduction of the three-body interaction. We conclude that the origin of the anomalous properties is that the transport process corresponding to bulk viscosity is a scalar process that does not involve directional flow, unlike other transport processes.