AB-INITIO MOLECULAR-DYNAMICS SIMULATION OF THE SOLVATION AND TRANSPORT OF H3O- IONS IN WATER( AND OH)

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 H3O+ ion a dynamic solvation complex which con tinuously fluctuates between a (H5O2)(+) and (H9O4)(+) structure as a result of proton transfer. The results of the simulation strongly sugg est that the rate-limiting step for the migration of the excess proton is the concerted dynamics of the second solvation shell hydrogen bond ed to the ligand H2O molecules. The OH- ion has a predominantly planar 4-fold coordination. Proton transfer is only observed when this (H9O5 )(-) complex is transformed into a tetrahedral (H7O4)(-) configuration . The formation of this more open complex determines the OH- diffusion rate.