Adsorption of water on sodium chloride surfaces: electrostatics – guided ab initio studies

Water adsorption is studied on medium-sized clusters of sodium chloride representing (100) and (110) surfaces at the ab initio level. Topographical features of molecular electrostatic potential (MESP) have been employed for predicting the potent sites for binding of one to four water molecules on these surfaces. Such guess geometries are initially optimized using an electrostatics-based model, electrostatic potential for intermolecular complexation (EPIC) and further at the Hartree–Fock and B3LYP/6-31G(d, p) levels. The corresponding interaction energies are examined for assessing co-operative binding effects. The geometry and interaction energy of four water molecules adsorbed on NaCl(100) clearly brings out the co-operative binding among the water molecules. Further, water binding to (110) surface is stronger than that with (100) surface. This is also in confirmation with the electrostatic properties of (110) surface. Many-body decomposition analysis brings out the stronger interaction between NaCl clusters with water molecules vis-a-vis water–water interaction.