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 Angstrom. 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 Angstrom. At this point and beyond, products are formed after the H3O+ or OH- hop so that they become separated by two solvation shells. (C) 1998 Elsevier Science B.V. All rights reserved.