Differential theory of fluids below the critical temperature : study of the Lennard-Jones fluid and of a model of C-60

The hierarchical reference theory (HRT) is applied to the Lennard-Jones fluid below the critical temperature T-c. This study completes a previous one performed above T-c using the same kind of approximate closure for the direct correlation function. Results for several thermodynamic quantities and for the two-particle correlations are reported and compared both with other theories and with simulation data. In the two-phase region the theory correctly yields rigorously hat isotherms; this feature allows a straightforward and accurate determination of the coexistence curve without resorting to the Maxwell construction. In the critical region our analysis is consistent with the previously developed one for T > T-c and displays nontrivial critical exponents. We also study a fluid with the Girifalco model potential for C-60. The critical point of the liquid-vapor transition is found at T-c = 2138 K and rho(c) = 0.50 nm(-3). When the HRT result is supplemented with Verlet's freezing criterion a triple point is found at T-t = 1979 K and rho(t) = 0.848 nm(-3).