Bridging scales from molecular simulations to classical thermodynamics: density functional theory of capillary condensation in nanopores

With the example of the capillary condensation of Lennard-Jones fluid in nanopores ranging from 1 to 10 nm, we show that the non-local density functional theory (NLDFT) with properly chosen parameters of intermolecular interactions bridges the scale gap from molecular simulations to macroscopic thermodynamics. On the one hand, NLDFT correctly approximates the results of Monte Carlo simulations (shift of vapour–liquid equilibrium, spinodals, density profiles, adsorption isotherms) for pores wider than about 2 nm. On the other hand, NLDFT smoothly merges (above 7–10 nm) with the Derjaguin– Broekhoff–de Boer equations which represent augmented Laplace–Kelvin equations of capillary condensation and desorption.