Analysis of the Dissociation of H₂O in Water Using First-Principles Molecular Dynamics

We have analyzed the structural, electronic, and dynamic properties along the reaction path of the dissociation of an H2O molecule in bulk water. There are four stages to the dissociation process, the last step being effected by a separation of hydroxyl and hydronium ions by two solvation shells. Structural as well as electronic data bear out this interpretation. In addition, by analyzing the electron localization function (ELF) around the oxygen in the hydroxyl ion, the question of why this species is most often 4-fold coordinated is addressed. The explanation arising from ELF is that unpaired electrons are symmetrically localized in a ring-shape around the O atom leading to the possibility of a planar solvation shell as observed in ab initio simulations. Finally, a dynamic analysis gives an indication of the femtosecond time-scale of the solvent response.