Universality in the structural change of expanded liquid alkali metals along the liquid-vapour coexistence curve

The structures of expanded liquid alkali metals, Na, K, Rb and Cs, along the liquid-vapour coexistence curve are investigated theoretically by employing the integral equation method in the modified hypernetted-chain (MHNC) approximation and the molecular dynamics (MD) simulation. Excellent agreement is obtained between the MHNC and the MD results, which also agree well with the experimental results. It is shown from these systematic investigations that the characteristic features of the density dependence of the structure along the liquid-vapour coexistence curve observed for expanded liquid Rb (Franz et al. 1980) and Cs (Winter et al. 1987) are common features for expanded liquid alkali metals.