Self-Energy and Excitonic Effects in the Electronic and Optical Properties of TiO2 Crystalline Phases

TL;DR

This study provides a comprehensive ab-initio analysis of TiO2's electronic and optical properties, including excitonic effects, offering new quantitative insights into its gaps and exciton localization in different crystalline phases.

Contribution

It presents the first detailed ab-initio evaluation of TiO2's electronic and optical gaps, including excitonic effects, with a unified theoretical approach.

Findings

Quantitative evaluation of electronic and optical gaps matching experimental data

Identification of exciton localization in rutile and anatase phases

First estimation of some properties for TiO2 using advanced many-body techniques

Abstract

We present a unified ab-initio study of electronic and optical properties of TiO2 rutile and anatase phases, with a combination of Density Functional Theory and Many Body Perturbation Theory techniques. The consistent treatment of exchange-correlation, with the inclusion of many body one-particle and two-particles effects in self-energy and electron-hole interaction, produces a high quality description of electronic and optical properties, giving, for some quantities, the first available estimation for this compound. In particular, we give a quantitative, direct evaluation of the electronic and direct optical gaps, clarifying their role with respect to previous values obtained by various experimental techniques. We obtain a description for both electronic gap and optical spectra that is consistent with experiments, analysing the role of different contributions to the experimental optical gap and relating them to the level of theory used in our calculations. We also show the spatial nature of excitons in the two crystalline phases, highlighting the localization character of different optical transitions. This paper aims at understanding and firmly establishing electro-optical bulk properties, so far not yet clarified, of this material of fundamental and technological interest for green energy applications.