Ab Initio Molecular Dynamics Simulation of the Solvation and Transport of Protonic Charge Defects in Water

Applying the ab initio molecular dynamics method we have studied the solvation and dynamics of an excess proton and a proton hole in liquid water. We find for the H(3)O+ ion a dynamic solvation complex which continuously fluctuates between a (H(5)O(2)+ and (H(9)O(4))+ structure as a result of proton transfer. The results of the simulation strongly suggest that the rate limiting step for the migration of the excess proton is the concerted dynamics of the second solvation shell hydrogen bonded to the ligand H2O molecules. The OH- ion has a predominantly planar fourfold coordination. Proton transfer is only observed when this (H(9)O(5))- complex is
transformed into a tetrahedral (H(7)O(4))- configuration. The formation of this more open complex determines the OH- diffusion rate.