Is the structure of hydroxide dihydrate OH−(H2O)2? An ab initio path integral molecular dynamics study

Abstract

We carried out ab initio path integral molecular dynamics simulations at room temperature for OH−(H2O) n (n = 1, 2) clusters to elucidate the ionic hydrogen bond structure with full thermal and nuclear quantum effects. We found that the hydrogen-bonded proton is located near the water molecule in the case of n = 2, while the proton is located at the center between hydroxide ion and the water molecule in the case of n = 1. Thus, the solvated hydroxide structure \({\text{HO}}{-}{\text{H}} \cdots{\text{OH}}\) is found in n = 2, while the proton sharing hydroxide structure \({\text{HO}} \cdots {\text{H}} \cdots {\text{OH}}\) is in n = 1. We found that the nature of hydrogen bonds significantly changes with the number of water molecules around the hydroxide. We also compared these results with those of F−(H2O) n (n = 1, 2) clusters.