Ab Initio van der Waals Interactions in Simulations of Water Alter Structure from Mainly Tetrahedral to High-Density-Like
Artikel i vetenskaplig tidskrift, 2011

The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations in the NVE ensemble using van der Waals (vdW) density-functional theory, i.e., using the new exchange-correlation functionals optPBE-vdW and vdW-DF2, where the latter has softer nonlocal correlation terms. Inclusion of the more isotropic vdW interactions counteracts highly directional hydrogen bonds, which are enhanced by standard functionals. This brings about a softening of the microscopic structure of water, as seen from the broadening of angular distribution functions and, in particular, from the much lower and broader first peak in the oxygen-oxygen pair-correlation function (PCF) and loss of structure in the outer hydration shells. Inclusion of vdW interactions is shown to shift the balance of resulting structures from open tetrahedral to more close-packed. The resulting O-O PCF shows some resemblance with experiment for high-density water (Soper, A. K.; Ricci, M.A. Phys. Rev. Lett. 2000, 84, 2881), but not directly with experiment for ambient water. Considering the accuracy of the new functionals for interaction energies, we investigate whether the simulation protocol could cause the deviation. An O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from low-density liquid water, as extrapolated from experiments, reproduces near-quantitatively the experimental O-O PCF for ambient water. This suggests the possibility that the new functionals maybe reliable and that instead larger-scale simulations in the NPT ensemble, where the density is allowed to fluctuate in accordance with proposals for supercooled water, could resolve the apparent discrepancy with the measured PCF.

liquid water

stokes-einstein relation


generalized gradient approximation

functional theory

radial-distribution functions




hydrogen-bond network

ambient conditions



A. Mogelhoj

Stanford Synchrotron Radiation Laboratory

Danmarks Tekniske Universitet (DTU)

A. K. Kelkkanen

Danmarks Tekniske Universitet (DTU)

K. T. Wikfedt

Stockholms universitet

J. Schiotz

Danmarks Tekniske Universitet (DTU)

J. J. Mortensen

Danmarks Tekniske Universitet (DTU)

L. G. M. Pettersson

Stockholms universitet

Bengt Lundqvist

Chalmers, Teknisk fysik, Material- och ytteori

K. W. Jacobsen

Danmarks Tekniske Universitet (DTU)

A. Nilsson

Stanford Synchrotron Radiation Laboratory

J. K. Norskov

Stanford Synchrotron Radiation Laboratory

Danmarks Tekniske Universitet (DTU)

Stanford University

Journal of Physical Chemistry B

1520-6106 (ISSN) 1520-5207 (eISSN)

Vol. 115 14149-14160


Fysikalisk kemi