Improvement in hydrogen bond description using van der Waals-corrected DFT: The case of small water clusters

The method recently developed to
include van der Waals interactions in DFT using Wannier
functions is applied to small water clusters,
characterized by Hydrogen-bonding interactions.
In particular, water
hexamer represents a critical test case since
it is relevant for the condensed phases of water
and has four low-energy isomers with similar binding energies.
We are able to achieve results
close to those obtained by high-level quantum chemistry methods
and we find that inclusion of
van der Waals effects is crucial for an appropriate
description of the Hydrogen bonds and to get accurate
dissociation-energy estimates.
The relevance of these results for DFT simulations of
liquid water is finally discussed.