Hydrogen bonding in liquid water: An ab initio QM/MM MD simulation study

Pattern and dynamics of hydrogen bonds in liquid water were investigated by a quantum mechanical/molecular mechanical molecular dynamics (QM/MM MD) simulation at Hartree-Fock (HF) level of theory. A large subregion of the whole system comprising two complete coordination shells was treated quantum mechanically in order to include all polarization and charge transfer effects and to obtain accurate data about structure and dynamics of the intermolecular bonds. The results of this investigation are in agreement with recent experimental findings and suggest that in liquid water every molecule forms in average 2.8, but almost as a rule less than four intermolecular hydrogen bonds.