Effect of Functional and Electron Correlation on the Structure and Spectroscopy of the Al2O3(001)-H2O Interface.

Effect of Functional and Electron Correlation on the Structure and Spectroscopy of the Al2O3(001)-H2O Interface.

Mark J. DelloStritto, Stephan M. Piontek, Michael L. Klein, and Eric Borguet
J. Phys. Chem. Lett. http://dx.doi.org/10.1021/acs.jpclett.9b00016.

Abstract
Oxide−water interfaces are ubiquitous, with many applications in industry and the environment, yet there is a great deal of controversy over their properties and microscopic structure. This controversy stems, in part, from the unique H-bond networks formed at different surface terminations and mineral compositions. Density functional theory simulations of these interfaces require an accurate description of both the oxide mineral and water in diverse H-bond environments. Thus, herein we simulate the Al2O3(001)−H2O interface using the PBE, PBE-TS, RPBE, SCAN, and HSE06-TS functionals to determine how calculated interfacial properties depend on the choice of functional. We find that the structure of the first few layers of water at the surface is determined by electron correlation in a way that cannot be approximated using semiemipirical van der Waals corrections. Of the functionals investigated, we find that SCAN yields the most accurate interfacial structure, dynamics, and sum frequency generation spectrum. Furthermore, SCAN leads to a reduction in the order of the 2D H-bond network of water at the alumina surface predicted by GGA functionals, leading to a significant decrease in the anisotropy of the diffusion coefficient at the surface. We emphasize the importance of using a functional which accurately describes electron correlation for more complex oxides, such as transition-metal oxides, where electron correlation may play an even greater role in determining the structure and dynamics of the oxide−water interface.

URL: http://dx.doi.org/10.1021/acs.jpclett.9b00016.

Importance of van der Waals Effects on the Hydration of Metal Ions from the Hofmeister Series

Importance of van der Waals Effects on the Hydration of Metal Ions from the Hofmeister Series

Liying Zhou, Jianhang Xu, Limei Xu, and Xifan Wu
J. Chem. Phys. 150, 124505 (2019).

Abstract
The van der Waals (vdW) interaction plays a crucial role in the description of liquid water. Based on ab initio molecular dynamics simulations, including the non-local and fully self-consistent density-dependent implementation of the Tkatchenko-Scheffler dispersion correction, we systematically studied the aqueous solutions of metal ions (K+, Na+, and Ca2+) from the Hofmeister series. Similar to liquid water, the vdW interactions strengthen the attractions among water molecules in the long-range, leading to the hydrogen bond networks softened in all the ion solutions. However, the degree that the hydration structure is revised by the vdW interactions is distinct for different ions, depending on the strength of short-range interactions between the hydrated ion and surrounding water molecules. Such revisions by the vdW interactions are important for the understanding of biological functionalities of ion channels.

URL: https://doi.org/10.1063/1.5086939

Active Learning of Uniformly Accurate Interatomic Potentials for Materials Simulation

Active Learning of Uniformly Accurate Interatomic Potentials for Materials Simulation

Linfeng Zhang, De-Ye Lin, Han Wang, Roberto Car, and Weinan E
Phys. Rev. Materials 3, 023804 (2019).

Abstract
An active learning procedure called deep potential generator (DP-GEN) is proposed for the construction of accurate and transferable machine learning-based models of the potential energy surface (PES) for the molecular modeling of materials. This procedure consists of three main components: exploration, generation of accurate reference data, and training. Application to the sample systems of Al, Mg, and Al-Mg alloys demonstrates that DP-GEN can produce uniformly accurate PES models with a minimal number of reference data.

URL: https://link.aps.org/doi/10.1103/PhysRevMaterials.3.023804

Structure, Polarization, and Sum Frequency Generation Spectrum of Interfacial Water on Anatase TiO2

Structure, Polarization, and Sum Frequency Generation Spectrum of Interfacial Water on Anatase TiO2

Marcos F. Calegari Andrade, Hsin-Yu Ko , Roberto Car and Annabella Selloni
J. Phys. Chem. Lett. 9, 6716 (2018).

Abstract
The photocatalytic activity of TiO2 for water splitting has been known for decades, yet the adsorption structure and hydrogen bonding of water at the interface with TiO2 have remained controversial. We investigate the prototypical aqueous interface with anatase TiO2 (101) using ab initio molecular dynamics (AIMD) with the strongly constrained and appropriately normed (SCAN) density functional, recently shown to provide an excellent description of the properties of bulk liquid water. We find that water forms a stable bilayer of intact molecules with ice-like dynamics and enhanced dipole moment and polarizability on the anatase surface. The orientational order and H-bond environment of interfacial water are reflected in the computed sum frequency generation (SFG) spectrum, which agrees well with recent measurements in the OH stretching frequency range (3000–3600 cm–1). Additional AIMD simulations for a model interface with 66% of dissociated water in the contact layer show that surface hydroxyls disrupt the order in the bilayer and lead to a much faster orientational dynamics of interfacial water. Nonetheless, the computed SFG spectrum for the hydroxylated surface also agrees with experiment, suggesting that SFG measurements in a wider frequency range would be necessary to unambiguously identify the character of interfacial water on anatase.

URL: https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.8b03103