Structure of Expanded Liquid Caesium in the Modified Hypernetted-Chain Approximation

The density dependence of the structure of expanded liquid caesium is studied theoretically from the melting point up to its critical point along the liquid-vapour coexistence curve. The structure factor and the pair distribution function are calculated in the modified hypernetted-chain (MHNC) approximation on the basis of the effective pair potentials obtained by the pseudopotential theory with two types of empty-core potentials. It is shown that the experimentally observed characteristic features of the structural change with decreasing density are well reproduced theoretically. In particular, the density dependences of the first peak and the low q behaviour of the structure factor and the coordination number are in good agreement with experiment.