Application of density functional perturbation theory to pure fluid liquid–vapor interfaces

Abstract

Common density functional theories often use the so-called mean-field approximation to the attractive term of the free energy, which is not accurate when compared with molecular dynamics simulations. We applied a modification of this attractive free energy term of a local density functional approach where an analytical representation of the radial distribution function is taken into account. A cutoff Lennard-Jones-12-6 potential, divided according to the Weeks-Chandler-Andersen prescription, is used as the intermolecular interaction force model. This density functional perturbation approach gives the correct phase quilibrium and predicts a surface tension in excellent agreement with recent molecular dynamics simulations. The surface tension of some pure simple fluids is predicted from an intrinsic contribution, obtained by the modified density functional perturbation theory, plus contributions due to capillary wave roughening of the surface. The respective Lennard-Jones potential parameters were obtained from fitting to saturated liquid densities of the pure fluids.

An accurate density functional theory for the vapor-liquid interface of associating chain molecules based on the statistical associating fluid theory for potentials of variable range

“…We have instead determined the vapor-liquid critical temperature T c for infinitely long chains and assumed a Guggenheim 11,91 correspondingstates law ␥ϭ␥ 0 (1ϪT/T c ) 1. 23 . The zero-temperature surface tension ␥ 0 was found to be practically constant (␥ 0 ϭ1.9 to within 1%͒ for systems with chain lengths of m ϭ1 to 10; this value was used to estimate ␥(T) in the limit m→ϱ.…”

“…Toxvaerd performed a full integration over the hard-sphere reference system using an average pair distribution function of the inhomogeneous system. Similar averaging procedures for the inhomogeneous correlation function of the reference system have now been employed by Carey et al, 20 Tang et al, 21 Sokolowski and Fischer, 22 Winkelmann and co-workers, 15,23 and by Tang and Wu. 24 Inhomogeneous systems of associating molecules have received particular attention in recent years.…”

“…[17][18][19] Though a mean-field treatment ͑in which the correlations are ignored͒ is more common, the approach has now been used by a number of other groups. 15,[20][21][22][23][24] We consider a simple arithmetic average of the density ¯ϭ͓ (r) ϩ (rЈ)͔/2 ͑also see Ref. 84͒.…”

Prediction of internal structure and properties in fluid model interfaces of binary and ternary liquid mixtures

“…Supposed that the interaction pair potential can be separated into a repulsive and an attractive term, the functional F ex [{ρ i }] can be expressed in a perturbation-like manner [2,4,5,8,[49][50][51] into a repulsive term F 0 and an attractive contribution F a :…”

Investigation of Surface Tensions for Pure Fluids outside and inside the Critical Region

“…In the recent years, interest increased rapidly in establishing a self-consistent thermodynamic framework under which both the phase equilibria and interfacial properties can be investigated within a single set of molecular parameters. Although this framework has been tested with success for fluids outside the critical region, [1][2][3] its application inside the critical region is challenging.…”