The effective pair potential of expanded liquid caesium obtained by the inverse method

The effective pair potentials phi(r) of liquid caesium for a wide range of density are derived from experimental structure factors using the inverse method, which is based on the integral equation theory and the molecular dynamics (MD) simulation. The results are discussed in comparison with those obtained previously for liquid rubidium and with those obtained by the pseudopotential perturbation theory. The density dependence of phi(r) derived for liquid caesium shows features in common with that for liquid rubidium: with decreasing density, the repulsive part of phi(r) becomes softer, its oscillation becomes smaller and then disappears and the resulting attractive part grows longer ranged. It is shown by comparing the corresponding states with the same scaled densities that the repulsive part of the phi(r) for caesium is softer than that for rubidium.