Perturbation Theories for the Thermodynamic Properties of Fluids and Solids

6 Perturbation Theories for Fluids and Solids

experimental data for some thermodynamic property. Restricting ourselves to neutral

nonpolar molecules interacting with each other by means of spherically symmetric

pair potentials u(r), the general features of the potential are as follows: it is positive

for r < σ, with a strongly negative slope, and negative for r > σ, so that it is null

for r =σ; it reaches its minimum value −ε at r =r

m

, and decays toward zero as

r →∞. Therefore, the intermolecular force F(r) =−du(r)/dr is strongly positive,

that is strongly repulsive, for r < r

m

, and negative, that is attractive, for r > r

m

,in

agreement with the considerations ...