The dissociation mechanism of H2O in water studied by first-principles molecular dynamics

We have performed a series of Car–Parrinello simulations to investigate the dissociation of H2O in water. An intramolecular O–H bond length was chosen as the reaction coordinate and its value was increased in increments of 0.1 Å. At each point along the reaction coordinate, time-averaged properties were determined and the free energy profile as a function of the reaction coordinate was calculated. The transition state corresponds to a value of the reaction coordinate of 1.7–1.8 Å. At this point and beyond, products are formed after the H3O+ or OH− hop so that they become separated by two solvation shells.