Effect of three-body interactions on Ar adsorption on graphitized carbon black

The Axilrod-Teller equation is incorporated into nonlocal density functional theory (NLDFT) to improve the description of low-temperature argon adsorption isotherm on graphitized carbon black. Using the NLDFT based on the Tarazona smoothed density approximation and the test-particle method, the pair and triplet distribution functions for liquid argon were analyzed. The latter allowed us to quantitatively account for the three-body Axilrod-Teller nonadditive term. An analogous scheme to that of Weeks, Chandler, and Andersen is proposed to incorporate the Axilrod-Teller equation into the NLDFT in the framework of mean field approximation. The three-body nonadditive term appeared to decrease the internal energy of liquid argon by about 5%, which is in agreement with molecular simulation results. The new approach has been applied to the vapor-liquid coexistence and to argon adsorption on graphitized carbon black at 87.3 K. The approach has been shown to fit the experimental adsorption isotherm within the relative error of about 4% as opposed to 37% in the case of the standard NLDFT. This is due to weakening of the intermolecular interaction potential by about 20% in the molecular layer nearest to the graphite surface resulted mainly from the positive Axilrod-Teller contribution of triplets comprising one carbon atom.