Dynamical Structure of Expanded Liquid Alkali Metals

We have investigated theoretically the temperature dependence of the dispersion relation, derived from the dynamical structure factor, of expanded liquid alkali metals on the basis of the effective pair potential obtained by the pseudopotential theory, the static structure factor calculated with the modified hypernetted-chain (MHNC) approximation and the dynamical structure factor calculated with the viscoelastic approximation. It is shown that the characteristic features of the observed temperature dependence of the dispersion relation of expanded liquid rubidium are well reproduced theoretically and that those features are common to all expanded liquid alkali metals. The quality of the viscoelastic approximation is assessed by comparing the theoretical results with those of the molecular dynamics simulation. The universal feature of the liquid alkali metals near the triple point is discussed by scaling the pair potential and the dispersion curve.