Bulk viscosity in a density-dependent-potential system

We derive a new formula for the bulk viscosity, ζ, which is expressed in terms of microscopic quantities such as interatomic potentials and pair distribution functions. This offers an outstanding advantage over previously proposed formulae where the bulk viscosity is expressed in terms of a macroscopic quantity, i.e., pressure. This new formula is derived by solving the time development equations of the pair distribution functions. We apply our formula to a system in which the interatomic potential depends on the density. We show that ζ increases in the region where the interatomic potential is density dependent. This result agree qualitatively with the experimental results for liquid mercury.