Density fluctuations in liquid rubidium. II. Molecular-dynamics calculations

Molecular-dynamics (MD) calculations on liquid rubidium at 46 °C and 1.502 g ${\mathrm{cm}}^{-3\mathrm{}}$ have been made using a suitable pair potential. Whereas for wave number $\kappa <1.2\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$ propagating density fluctuations were obtained, only overdamped nonpropagating fluctuations are found for larger $\kappa$. For all $\kappa$ there is good agreement with recent neutron inelastic-scattering experiments. The mean-square acceleration given by MD is found to be much larger than the value derived from another neutron experiment extending over $\kappa =4\mathrm{} \mathrm{to} 8$ ${\mathrm{\AA }}^{-1\mathrm{}}$; the reason for the discrepancy is analyzed to show that the neutron-scattering data cannot be interpreted in terms of the mean-square acceleration alone.