To understand anomalous energetics and dynamics in water, nuclear quantum effects such as zero-point energy and delocalization of wave packets (WPs) representing water hydrogen atoms should be essential. However, since quantum calculations of many-body dynamics are highly complicated in general, none has yet directly viewed the quantum WP dynamics of hydrogen atoms in liquid water. Our semiquantum molecular dynamics simulation for the first time made it possible to observe the hydrogen WP dynamics in liquid water. Here, we demonstrate that the microscopic WP dynamics are closely correlated to and play key roles in the dynamical rearrangements in the hydrogen-bond network (HBN) of liquid water. Especially, the memory loss of the dipolar angle formed by two waters is accelerated with the nuclear quantum effect introduced by the nuclear WP, rationalizing the faster memory decay of the HBN in the quantum liquid water. We found the quantum effects of hydrogen atoms on mesoscopic liquid water behaviors such as intermittent collective motions associated with the rearrangement of HBN and the concomitant fluctuation and relaxation. Our results will provide new physical insights on HBN dynamics in water whose significance is not limited to the pure liquid dynamics but also for understanding chemical and biological reactions in liquid water.
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