Density, structure, and dynamics of water: The effect of van der Waals interactions

Abstract

It is known that ab initio molecular dynamics (AIMD) simulations of liquid water at ambient conditions, based on the generalized gradient approximation (GGA) to density functional theory (DFT), with commonly used functionals fail to produce structural and diffusive properties in reasonable agreement with experiment. This is true for canonical, constant temperature simulations where the density of the liquid is fixed to the experimental density. The equilibrium density, at ambient conditions, of DFT water has recently been shown by Schmidt et al. [J. Phys. Chem. B, 113, 11959 (2009)] to be underestimated by different GGA functionals for exchange and correlation, and corrected by the addition of interatomic pair potentials to describe van der Waals (vdW) interactions. In this contribution we present a DFT-AIMD study of liquid water using several GGA functionals as well as the van der Waals density functional (vdW-DF) of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. As expected, we find that the density of water is grossly underestimated by GGA functionals. When a vdW-DF is used, the density improves drastically and the experimental diffusivity is reproduced without the need of thermal corrections. We analyze the origin of the density differences between all the functionals. We show that the vdW-DF increases the population of non-H-bonded interstitial sites, at distances between the first and second coordination shells. However, it excessively weakens the H-bond network, collapsing the second coordination shell. This structural problem is partially associated to the choice of GGA exchange in the vdW-DF. We show that a different choice for the exchange functional is enough to achieve an overall improvement both in structure and diffusivity.

A thermodynamic adsorption/entrapment model for selenium(IV) coprecipitation with calcite

“…The plane--wave cutoff energy remained at 810 eV. As recent work has shown that the 650 description of water in DFT calculations is improved by the inclusion of corrections for the long--range 651 dispersion (Wang et al, 2011), the calculations of the SeO 3 2--incorporation at the calcite--water interface 652 were additionally studied with the PBE+D--USP method, where dispersion corrections are included 653 according to the method of Tkatchenko and Scheffler (2009). As our previous calculations revealed 654 periodicity in the structure of the water layer, the water--interface incorporation was modeled using 655 PBE+D for the two distinct sites, Se1 and Se2.…”

Water: one molecule, two surfaces, one mistake

“…35 and some examples for water within the approach B can be found in Ref. 36,37 . Notice that in approaches A and B, the energy is obtained "on the fly" for each configuration either by solving the Schrödinger equation or by performing density functional theory (DFT) calculations.…”

The structure of ionic aqueous solutions at interfaces: An intrinsic structure analysis

“…Similarly, AI-DFT computations of water predict structural and coexistence properties that differ from those of experiment, highlighting the need for significant advances in the development of functionals that handle more accurately dispersive interactions. 46 In this paper, we employ point charge models. Given the wide range of studies performed with this approach, they provide a good starting point to address the main aim of this paper, namely, the computation of intrinsic interfacial structure, and to obtain a qualitative view of the structure of interfacial solutions for a wide range of salt conditions.…”