The Combined Influence of Nuclear Quantum Effects and van der Waals   Interactions on the Structure of Ambient Water
  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. 
Jeffrey M. McMahon, Miguel A. Morales, Brian Kolb, and Timo Thonhauser
physics.chem-ph cond-mat.mtrl-sci