Ab initio van der Waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like (original) (raw)
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The Journal of Chemical Physics, 2015
We investigate the structural properties of liquid water at near ambient conditions using first-principles molecular dynamics simulations based on a semilocal density functional augmented with nonlocal van der Waals interactions. The adopted scheme offers the advantage of simulating liquid water at essentially the same computational cost of standard semilocal functionals. Applied to the water dimer and to ice I h , we find that the hydrogen-bond energy is only slightly enhanced compared to a standard semilocal functional. We simulate liquid water through molecular dynamics in the N pH statistical ensemble allowing for fluctuations of the system density. The structure of the liquid departs from that found with a semilocal functional leading to more compact structural arrangements. This indicates that the directionality of the hydrogenbond interaction has a diminished role as compared to the overall attractions, as expected when dispersion interactions are accounted for. This is substantiated through a detailed analysis comprising the study of the partial radial distribution functions, various local order indices, the hydrogen-bond network, and the selfdiffusion coefficient. The explicit treatment of the van der Waals interactions leads to an overall improved description of liquid water. Recently, several nonlocal formulations have been introduced which explicitly account for van der Waals interactions through a functional of the density. 15,17,19,24 Among these, the one proposed by Vydrov and Van Voorhis 19 in its revised form denoted rVV10 carries the
arXiv (Cornell University), 2014
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.
Journal of Chemical Physics, 2008
Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10-15 meV/ H 2 O. These reference data are then used to evaluate the performance of several density-functional theory exchange-correlation ͑xc͒ functionals. A subset of the xc functionals tested for smaller water clusters ͓I. Santra et al., J. Chem. Phys. 127, 184104 ͑2007͔͒ has been considered. While certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers ͑coming within 10-20 meV/ H 2 O͒, none predict the correct energetic ordering of the four isomers nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals ͑dispersion͒ forces in the xc functionals considered. It is shown that the addition of an empirical pairwise ͑attractive͒ C 6 R −6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.
Density-functional theory exchange-correlation functionals for hydrogen bonds in water
Hydrogen bonds (HBs) involving water molecules are ubiquitous in nature. However an accurate description of HBs with simulation techniques, including even quantum mechanical approaches such as density-functional theory (DFT), is a major challenge. Mainly because of a good balance between computational cost and accuracy, DFT has been routinely applied to study water in various environments, for example, liquid water, ice, adsorbed, and confined water, yet how well DFT exchange-correlation (xc) functionals describe HBs between water molecules is unknown and indeed controversial. To address this issue a series of systematic studies on water from different environments (representative of gas phase clusters, liquid water, and various phases of ice) have been performed with a range of DFT xc functionals and, in principle, more accurate explicitly correlated quantum chemistry methods.
Molecular Density Functional Theory of Water
The Journal of Physical Chemistry Letters, 2013
Three-dimensional implementations of liquid-state theories offer an efficient alternative to computer simulations for the atomic-level description of aqueous solutions in complex environments. In this context, we present a (classical) molecular density functional theory (MDFT) of water that is derived from first principles and is based on two classical density fields, a scalar one, the particle density, and a vectorial one, the multipolar polarization density. Its implementation requires as input the partial charge distribution of a water molecule and three measurable bulk properties, namely, the structure factor and the k-dependent longitudinal and transverse dielectric constants. It has to be complemented by a solute−solvent threebody term that reinforces tetrahedral order at short-range. The approach is shown to provide the correct 3-D microscopic solvation profile around various molecular solutes, possibly possessing H-bonding sites, at a computer cost two to three orders of magnitude lower than with explicit simulations.
Two exchange-correlation functionals compared for first-principles liquid water
Molecular Simulation, 2005
The first-principles description of liquid water using ab initio molecular dynamics (AIMD) based on Density Functional theory (DFT) has recently been found to require long equilibration times, giving too low diffusivities and a clear over-structuring of the liquid. In the light of these findings we compare here the room-temperature description offered by two different exchange correlation functionals: BLYP, the most popular for liquid water so far, and RPBE, a revision of the widely used PBE. We find for RPBE a less structured liquid with radial distribution functions closer to the experimental ones than the ones of BLYP. The diffusivity obtained with RPBE for heavy water is still 20% lower than the corresponding experimental value, but it represents a substantial improvement on the BLYP value, one order of magnitude lower than experiment. These characteristics and the hydrogen-bond (HB) network imperfection point to an effective temperature ∼3% lower than the actual simulation temperature for the RPBE liquid, as compared with BLYP's ∼17% deviation. The too long O-O average nearest-neighbor distance observed points to an excessively weak HB, possibly compensating more fundamental errors in the DFT description.
A Molecular Density Functional Theory of Water
2016
Three dimensional implementations of liquid state theories offer an efficient alternative to computer simulations for the atomic-level description of aqueous solutions in complex environments. In this context, we present a (classical) molecular density functional theory (MDFT) of water that is derived from first principles and is based on two classical density fields, a scalar one, the particle density, and a vectorial one, the multipolar polarization density. Its implementa-tion requires as input the partial charge distribution of a water molecule and three measurable bulk properties, namely the structure factor and the k-dependent lon-gitudinal and transverse dielectric constants. It has to be complemented by a solute-solvent three-body term that reinforces tetrahedral order at short range. The approach is shown to provide the correct three-dimensional microscopic sol-vation profile around various molecular solutes, possibly possessing H-bonding sites, at a computer cost two-three...
The Journal of Physical Chemistry Letters
Density functional theory-based molecular dynamics simulations are increasingly being used for simulating aqueous interfaces. Nonetheless, the choice of the appropriate density functional, critically affecting the outcome of the simulation, has remained arbitrary. Here, we assess the performance of various exchange−correlation (XC) functionals, based on the metrics relevant to sum-frequency generation spectroscopy. The structure and dynamics of water at the water−air interface are governed by heterogeneous intermolecular interactions, thereby providing a critical benchmark for XC functionals. We find that the XC functionals constrained by exact functional conditions (revPBE and revPBE0) with the dispersion correction show excellent performance. The poor performance of the empirically optimized density functional (M06-L) indicates the importance of satisfying the exact functional condition. Understanding the performance of different XC functionals can aid in resolving the controversial interpretation of the interfacial water structure and direct the design of novel, improved XC functionals better suited to describing the heterogeneous interactions in condensed phases.
The Journal of Chemical Physics, 1996
The structure, dynamical, and electronic properties of liquid water utilizing different hybrid density functionals were tested within the plane wave framework of first-principles molecular dynamics simulations. The computational approach, which employs modified functionals with short-ranged Hartree-Fock exchange, was first tested in calculations of the structural and bonding properties of the water dimer and cyclic water trimer. Liquid water simulations were performed at the state point of 350 K at the experimental density. Simulations included three different hybrid functionals, a meta-functional, four gradient-corrected functionals, and the local density and Hartree-Fock approximations. It is found that hybrid functionals are superior in reproducing the experimental structure and dynamical properties as measured by the radial distribution function and self-diffusion constant when compared to the pure density functionals. The local density and Hartree-Fock approximations show strongly over-and understructured liquids, respectively. Hydrogen bond analysis shows that the hybrid functionals give slightly smaller average numbers of hydrogen bonds than pure density functionals but similar hydrogen bond populations. The average molecular dipole moments in the liquid from the three hybrid functionals are lower than those of the corresponding pure density functionals. † Part of the special issue "Michael L. Klein Festschrift".