Thermodynamic properties of molecules interacting with inverse power potentials

The thermodynamic properties of soft-sphere molecules are analyzed using differential equations. The analysis is extended to multi-term inverse-power potentials by introducing an approximation which isexact for soft spheres. The approximation is tested using the Lennard-Jones equation of state which is found most accurate at high densities. The analysis suggests a simple non-perturbation method of combiningthe contributions from different inverse-power terms to obtain the thermodynamic properties for molecules interacting with multi-term potentials.