High-temperature dynamic behavior in bulk liquid water: A molecular dynamics simulation study using the OPC and TIP4P-Ew potentials

摘要

Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water,specifically the behavior of the diffusion coefficient,hydrogen bond,and nearest-neighbor lifetimes.Two water potentials were compared:the recently proposed "globally optimal" point charge (OPC) model and the well-known TIP4P-Ew model.By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants,a crossover from Vogel-Fulcher Tammann behavior to a linear trend with increasing temperature was detected at T* ≈ 309 and T* ≈ 285 K for the OPC and TIP4P-Ew models,respectively.Experimentally,the crossover point was previously observed at T* ≈ 315 ± 5 K.We also verified that for the coefficient of thermal expansion αp(T,P),the isobaric αP(T) curves cross at about the same T* as in the experiment.The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross near T*,where the lifetimes are about 1 ps.For T ＜ T*,hydrogen bonds persist longer than nearest neighbors,suggesting that the hydrogen bonding network dominates the water structure at T ＜ T*,whereas for T ＞ T*,water behaves more like a simple liquid.The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.