Water reactions on reconstructed rutile TiO$_2$: a DFT / DFTB approach

TL;DR

This study compares DFT and DFTB methods to model water interactions on rutile TiO₂ surfaces, highlighting DFTB's strengths and limitations, and explores surface reconstruction and water splitting phenomena.

Contribution

It demonstrates the effectiveness of DFTB in modeling TiO₂/water interfaces and investigates surface reconstruction and water splitting using DFT predictions.

Findings

DFTB accurately describes static geometries of TiO₂/water interfaces.

DFTB requires improvements to match DFT in water dissociation predictions.

Surface reconstruction occurs at predicted temperatures, facilitating water splitting.

Abstract

Far from being conclusively understood, the reactive interaction of water with rutile does still present a challenge to atomistic modelling techniques rooted on quantum mechanics. We show that static geometries of stoichiometric TiO$_2$/water interfaces can be described well by Density Functional Tight Binding (DFTB). However, this method needs further improvements to reproduce the low dissociation propensity of H$_2$O after adsorption predicted by Density Functional Theory (DFT). A reliable description of the surface reactivity of water is fundamental to investigate the non-stoichiometric reconstruction of the (001) facet rich in Ti interstitials. Calculations based on (DFT) predict the transition temperature for the onset of reconstruction in remarkable agreement with experiments and suggest that this surface, in contact with liquid water, can promote spontaneous H$_2$O splitting and formation of H$_2$ molecules.