Ab initio molecular dynamics of expanded liquid sodium

The properties of liquid sodium have been studied using ab initio molecular dynamics over a wide range of temperatures and pressures. When expanded along the liquid-vapor coexistence curve, the de conductivity and average number of nearest neighbors decrease, as has been observed for other alkali metals. There is a sharp drop in the de conductivity when the density decreases from 0.31 to 0.16 g/cm(3). For densities at or below the latter value, the sodium vapor was observed to partially condense into a small fraction of the supercell simulation volume. This condensation was accompanied by aggregation of sodium atoms, but the lifetimes of these clusters are less than the vibrational period of the sodium dimer, indicating that they are short-lived transient associates, not molecular clusters in the traditional sense. [S0163-1829(98)50242-1].