Triple-dipole dispersion forces in dense fluids

Abstract

The contribution of triple-dipole dispersion forces to thermodynamic properties of fluid argon is determined from an analysis of computer-generated configurations of atoms. For states of liquid argon lying near the liquid-vapour equilibrium line the effect of triple-dipole interactions is to increase both internal energy and volume by several per cent. The inclusion of the triple- dipole contribution largely accounts for the discrepancies which are found between the experimental values of internal energy and pressure and the values calculated from a potential chosen to simulate the true pair potential between argon atoms. Accurate values are also obtained for the contribution of the triple-dipole potential to medium-dependent effective pair potentials of the type developed by Sinanoglu (1967). Results are given in tabular form for six states of fluid argon and for the corresponding states of krypton and xenon.