Molecular Dynamics Study of Temperature Effects on Water Structure and Kinetics

For a system of 216 water molecules, molecular dynamics calculations have been carried out at two temperatures in addition to the one studied and reported previously. As before, the Ben-Naim and Stillinger effective pair potential was used for these calculations. The results document the breakdown of hydrogen-bond order and the rapid increase in the freedom of molecular motions that accompany temperature rise in real water. We find no evidence at any temperature to support those water models which partition molecules into two classes (bonded framework or cluster molecules vs unbonded molecules). Nevertheless the pair potential distribution function changes with temperature in such a way as to suggest a basic hydrogen-bond rupture mechanism characterized by an excitation energy of about 2.5 kcal/mole. Some results indicate that the potential utilized is a bit too tetrahedrally directional to represent real water faithfully, so a possible modification is mentioned.