Adsorption of water on NaNO₃(001) surface from first-principles calculations

Density functional theory (DFT) calculations were applied to investigate the adsorption of water monomer, water clusters on NaNO₃(001) surface. Single water molecule is more likely to locate on the bridge site with its H atom attracted by the O atom of nitrate ion and its O atom adjacent to Na⁺. Mulliken population analysis shows that fewer electrons transfer from the Na atom of substrate to water molecule. A systematic study of water clusters adsorption at high coverages ranging from 0.5 monolayer (ML), 0.75ML, 1ML, 1.25ML, and 1.5ML on NaNO₃(001) surface was also investigated, and the results indicate that for 1ML water adsorption on NaNO₃(001) surface, a water chain is formed among four water molecules through hydrogen bonds. Interestingly, the water molecules are linked through hydrogen bonds to form a 14-membered macrocyclic water ring for 1.5ML adsorption on NaNO₃(001) surface. Our estimated O-H symmetric stretching frequency (ν_O-H) will have blueshift with decrease of water coverage, which is consistent with the tendency given by experiments.