We have developed a self-consistent description of an interface between a metal and a molecular liquid by combination of the density functional theory in the Kohn-Sham formulation ͑KS DFT͒ for the electronic structure, and the three-dimensional generalization of the reference interaction site model ͑3D RISM͒ for the classical site distribution profiles of liquid. The electron and classical subsystems are coupled in the mean field approximation. The procedure takes account of many-body effects of dense fluid on the metal-liquid interactions by averaging the pseudopotentials of liquid molecules over the classical distributions of the liquid. The proposed approach is substantially less time-consuming as compared to a Car-Parrinello-type simulation since it replaces molecular dynamics with the integral equation theory of molecular liquids. The calculation has been performed for pure water at normal conditions in contact with the ͑100͒ face cubic centered ͑fcc͒ surface of a metal roughly modeled after copper. The results are in good agreement with the Car-Parrinello simulation for the same metal model. The shift of the Fermi level due to the presence of water conforms with experiment. The electron distribution near an adsorbed water molecule is affected by dense water, and so the metal-water attraction follows the shapes of the metal effective electrostatic potential. For the metal model employed, it is strongest at the hollow site adsorption positions, and water molecules are adsorbed mainly at the hollow and bridge site positions rather than over metal atoms. Layering of water molecules near the metal surface is found. In the first hydration layer, adsorbed water molecules are oriented in parallel to the surface or tilted with hydrogens mainly outwards the metal. This orientation at the potential of zero charge agrees with experiment.

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We adapt the three-dimensional reference interaction site model (3D-RISM) to calculate the potentials of mean force for ion–molecular solution as a difference between the chemical potential of solvation of a cluster of solutes and of individual ones. The method yields the solvation structure around the cluster of solutes in detail. The solvation chemical potential is obtained for the three-dimensional hypernetted chain (3D-HNC) closure as well as for its partial linearization (3D-PLHNC approximation). The solvation chemical potential is obtained in a closed analytical form for both the 3D-HNC and 3D-PLHNC closures. The 3D-RISM integral equations are solved by using the supercell technique. A straightforward supercell treatment of ionic solute in polar molecular solvent leads to a big error in the potential of mean force as well as the solvation chemical potential, which for simple ions in water amounts to about 35 kcal/mol. We elaborated corrections to the 3D-RISM integral equations, alleviating the artifact of the supercell periodicity with an accuracy of 0.05 kcal/mol or better and restoring the long-range asymptotics of the solute–solvent correlation functions. The dielectrically consistent site–site RISM/HNC theory (DRISM/HNC) is employed for the solvent correlations to provide a proper description of the dielectric properties of solution. This allowed us to extend the description to solution at a finite salt concentration. We converge both the 3D-RISM and site–site DRISM integral equations by using the method of modified direct inversion in the iterative subspace. Owing to the proper initial guess of the correlation functions, iteration begins at once for a given temperature and full molecular charge, avoiding a gradual decrease of the temperature and increase of the site charges, which greatly reduces the computation time. We calculate and discuss the potentials of mean force for sodium chloride in ambient water at infinite dilution as well as at a finite concentration.

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