  Path-integral molecular dynamics simulations based on density functional
theory employing exchange-correlation density functionals capable of treating
nonlocal van der Waals (vdW) interactions self-consistently provide a
remarkably accurate description of ambient water. Moreover, they suggest that
water's structure may be impacted by a combined influence between nuclear
quantum effects and vdW interactions. The latter strongly favor the formation
of a high-density liquid, whereas the inclusion of the former mitigates this by
decreasing the mean hydrogen-bond (H-bond) distance. Examining the structure of
water reveals that while the major fraction of molecules do in fact exhibit the
traditional picture of near-tetrahedral coordination, the liquid considerably
softer than previously simulations have suggested, including a much lower
proportion of molecules double-donating H-bonds as well as a much larger
distribution of their angles.
