MOLECULAR-DYNAMICS OF AN EXCESS PROTON IN WATER USING A NONADDITIVE VALENCE-BOND FORCE-FIELD

We introduce a valence-bond-based semi-empirical Hamiltonian for descr ibing the dynamics of an excess proton in water. The model includes an arbitrary number N of valence states and the ground electronic state is obtained by diagonalization of the resulting N x N valence bond mat rix. The force field thus obtained is non-additive and allows for the delocalization of the excess protonic charge over several surrounding water molecules. This force field is used to perform simulated anneali ng optimizations and molecular dynamics simulations at finite temperat ures in order to investigate the structural and dynamical properties o f small H+(H2O)(n) clusters, as well as proton transfer dynamics along a H13O6+ structure in liquid water. (C) 1997 Elsevier Science B.V.