On the phase equilibrium of atomic and molecular pure fluids from thermodynamic perturbation theory

A simplified perturbation theoretical approach is presented for calculating the fluid phase behaviour of both atomic and molecular pure fluids. For atomic Lennard–Jones pure fluids, calculated critical points and vapour–liquid equilibrium coexistence curves show close agreement with computer simulations. For molecular fluids, the approach applied to quadrupolar fluids predicts the behaviour found in computer simulations for fluids with quadrupolar strength of q*2 = 1, 1.5, 2 and 2.5.