title: Nuclear quantum effects and hydrogen bond fluctuations in water.
abstract: The hydrogen bond (HB) is central to our understanding of the properties of water. However, despite intense theoretical and experimental study, it continues to hold some surprises. Here, we show from an analysis of ab initio simulations that take proper account of nuclear quantum effects that the hydrogen-bonded protons in liquid water experience significant excursions in the direction of the acceptor oxygen atoms. This generates a small but nonnegligible fraction of transient autoprotolysis events that are not seen in simulations with classical nuclei. These events are associated with major rearrangements of the electronic density, as revealed by an analysis of the computed Wannier centers and (1)H chemical shifts. We also show that the quantum fluctuations exhibit significant correlations across neighboring HBs, consistent with an ephemeral shuttling of protons along water wires. We end by suggesting possible implications for our understanding of how perturbations (solvated ions, interfaces, and confinement) might affect the HB network in water.
authors.affiliation: Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom.
authors.forename: Michele
authors.initials: M
authors.lastname: Ceriotti
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cuny
authors.forename: Michele
authors.initials: M
authors.lastname: Parrinello
authors.forename: David E
authors.initials: DE
authors.lastname: Manolopoulos
keywords: ab initio liquid water; generalized Langevin equation thermostat; path integral molecular dynamics