Insights into reactivity and defect properties of semiconductor surfaces from first-principles computations

Abstract

We use first-principles computations based on Ehrenfest dynamics and density functional theory to study water and methanol photo-oxidation on a model photo-catalytic material – the (110) surface of rutile titanium dioxide. We simulate photo-excitation in titania and the subsequent excited-state reaction trajectories. Analysis of the coupled dynamics of the electronic and ionic subsystems allows us to establish a novel reaction mechanism, for which we propose the name “photo-induced C-H acidity.” We provide a detailed and intuitive interpretation of the mechanism in terms of Lewis structures, identify the driving forces of the process, and propose general design principles for efficient photo-catalytic systems. Another important factor in the reactivity of semiconductor catalysts is the presence of defects in surface and subsurface regions. Knowledge of the formation energies of defects and impurities in different charge states is required in order to obtain insight into their concentration and stability. We develop an internally consistent method for calculating formation energies of charged defects based on density functional theory, which is applicable to both surface regions of semiconducting materials and two-dimensional materials. We discuss the implementation and usage details of the method and provide an example of its usage for studying sulfur vacancy formation in MoS2 monolayer.