Electron Dynamics of Solvated Ti(OH)₄

Abstract

Increasing interest in the photocatalytic activity of TiO₂ has led to considerations of using TiO₂ nanoparticles in energy generation. In order to better understand the electron-hole relaxation of nano scale TiO₂ structures, it is important to start with an understanding of TiO₂ synthesis building blocks. The solvated titanium (IV) ion is a precursor found in synthesis methods of colloidal TiO₂ nanostructures. This simplest test compound may reflect some common basic electronic features for larger structures composed of Ti(IV) coordinated with oxygen. For this computational study, a model of Ti(OH)₄ with tetrahedral coordination was created. To simulate the electronic properties of a solution of Ti(IV), the model was surrounded with 27 H₂O molecules. The model was explored by means of standard density functional theory (DFT) molecular dynamics (MD) followed by nonadiabatic electron dynamics computed with Reduced Density Matrix approach combined with “on-the-fly coupling”. Results were generated with Vienna ab initio Simulation Package (VASP) using the Perdew-Burke-Ernzerhof (PBE) functional, plane wave basis set, and projector augmented wave (PAW) potentials. The absorption spectra, MD, and electron-hole relaxation rates are presented for the Ti(OH)₄ model at various ambient temperatures. The electron-hole relaxation rates show a non-linear dependence on temperature and were found to be near the same order of magnitude as electron-hole relaxation rates in bulk TiO₂ calculations. A video of the geometry optimization can be found online.[1]