Collective motions in classical liquids. IV. Liquid rubidium

The coherent scattering function is calculated for liquid rubidium at its melting point on the basis of the theory developed in paper II of this series and using the static structure factor obtained by Rahman from computer simulation with a potential determined by Price et al. It is noted that for $q$ up to 1 ${\mathrm{\AA }}^{-1\mathrm{}}$, the theory indicates the existence of propagating density waves unlike liquid argon, but the shape of $S(q, \omega )$ is found to disagree with the experimental observations. For intermediate values of $q$, the agreement between the theoretical and experimental results is not so good, but the disagreement is always less than 40%. However, for $q\ge 3$ ${\mathrm{\AA }}^{-1\mathrm{}}$, the theoretical results for $S(q, \omega )$ are quantitatively in good agreement with the recent neutron inelastic-scattering measurements on liquid rubidium.