  A semi-empirical equation of state is presented for the liquid rubidium
metal. The Lennard-Jones (8.5-4) potential model, which originally has been
derived for liquid cesium metal, is found to be suitable for modeling of liquid
rubidium metal as well. By applying the experimental PVT data of compressed
liquid metal in the range 500 K to 1600 K, the slope B, and intercept C, of the
linear isotherms are determined and accordingly parameters of the potential
function are calculated. The contribution of non-spherical part of the
interaction potential to the second virial coefficient B2ns, is calculated by
using the Boltzman factor that involves the proposed model potential. The
multipole moments, standing as approximation of the non-spherical contribution
by multipole expansion, are calculated by the Gaussian 98W program at the B3LYP
level of theory. It can be concluded that the slope of the isotherm conforms to
B2ns quite well, though some deviations at low T's exist.
