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

Abstract

Molecular-dynamics (MD) calculations on liquid rubidium at 46 \ifmmode^\circ\else\textdegree\fi{}C and 1.502 g ${\mathrm{cm}}^{\ensuremath{-}3}$ have been made using a suitable pair potential. Whereas for wave number $\ensuremath{\kappa}l1.2$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ propagating density fluctuations were obtained, only overdamped nonpropagating fluctuations are found for larger $\ensuremath{\kappa}$. For all $\ensuremath{\kappa}$ 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 $\ensuremath{\kappa}=4 \mathrm{to} 8$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$; 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.