Nonlocal density functional theory of water taking into account many-body dipole correlations: binodal and surface tension of ‘liquid–vapour’ interface

Abstract

In this paper we formulate a nonlocal density functional theory of inhomogeneous water. We model a water molecule as a couple of oppositely charged sites. The negatively charged sites interact with each other through the Lennard–Jones potential (steric and dispersion interactions), square-well potential (short-range specific interactions due to electron charge transfer), and Coulomb potential, whereas the positively charged sites interact with all types of sites by applying the Coulomb potential only. Taking into account the nonlocal packing effects via the fundamental measure theory, dispersion and specific interactions in the mean-field approximation, and electrostatic interactions at the many-body level through the random phase approximation, we describe the liquid–vapour interface. We demonstrate that our model without explicit account of the association of water molecules due to hydrogen bonding and with explicit account of the electrostatic interactions at the many-body level is able to describe the liquid–vapour coexistence curve and the surface tension at the ambient pressures and temperatures. We obtain very good agreement with available in the literature MD simulation results for density profile of liquid–vapour interface at ambient state parameters. The formulated theory can be used as a theoretical background for describing of the capillary phenomena, occurring in micro- and mesoporous materials.

On the equivalence of self-consistent equations for nonuniform liquids: a unified description of the various modifications

“…Many studies on dense uniform liquids have demonstrated the dominant role of shortranged harshly repulsive intermolecular forces in determining structural correlations, which provides the insight that attractive intermolecular forces essentially cancel due to the symmetric configurations of molecules in uniform liquids [1][2][3]. In contrast, translational invariance of molecular arrangements is broken in non-uniform liquids [4][5][6][7][8][9][10][11][12]. Accordingly, both attractive and repulsive forces can, for instance, significantly influence the structure of a Lennard-Jones (LJ) fluid next to a hard wall because the vector sums of the long-range attractive forces do not cancel each other.…”

“…There are several situations in which such non-uniform states of liquid molecules emerge. Inhomogeneities occur [4][5][6][7][8][9][10][11][12]: (i) at interfaces between liquid-gas, liquid-liquid, and liquid-crystal phases; (ii) in the adsorption of liquids at solid substrates or walls; (iii) for fluids in confining geometries, such as slits and pores; and (iv) in the sedimentation equilibrium of colloidal particles under gravity. Theoretically, a non-uniform state can be created by adding an interaction potential term associated with an external field.…”

“…Theoretically, a non-uniform state can be created by adding an interaction potential term associated with an external field. For example, an external field may represent the presence of walls, slits, or pores [4][5][6][7][8][9][10][11][12][13][14]. We can also find adequate fields that are not only responsible for shifts and rounding of bulk phase transitions, but also induce wetting or drying transitions and related phenomena such as capillary condensation.…”

“…We can also find adequate fields that are not only responsible for shifts and rounding of bulk phase transitions, but also induce wetting or drying transitions and related phenomena such as capillary condensation. Furthermore, an external field is able to describe the interactions of fixed solutes with solvent liquids that significantly perturb the solvent density around solutes [4][5][6][7][8][9][10][11][12][13][14].…”

“…Based on this theoretical approach, we can evaluate the solvation free energy per solute and effective interaction potential between solutes [1,[4][5][6][7][8][9][10][11][12][13][14]. Specifically, the solvation thermodynamics in charged and polar systems underlies important processes in biology, including protein folding and ligand binding [13,14].…”