A density-functional theory for bulk and inhomogeneous Lennard-Jones fluids from the energy route

A new density-functional theory is developed for representing the structural and thermodynamic properties of Lennard-Jones fluids by unifying the modified fundamental measure theory for the short-range repulsion and the first-order mean-spherical approximation (FMSA) via the energy route for the attractive part of the intermolecular potential. This theory significantly improves the conventional mean-field approximation for the attractive forces and is applicable to both bulk and inhomogeneous systems using a single set of molecular parameters. The new theory is computationally very affordable and self-consistent with FMSA for bulk systems. It provides accurate radial distribution function, phase diagram, saturation pressure, and chemical potential of bulk Lennard-Jones fluids except very close to the critical point. In addition, it agrees well with simulation results for inhomogeneous systems including the adsorption isotherms and the density profiles of Lennard-Jones molecules near hard walls as well as in attractive slit pores.