Method development for the DFT calculation of charge-assisted surface reactions in a periodic model

Abstract

Many important processes of great technological importance can be modeled by properly designed charged systems. A common example is photocatalysis, where photon absorption promotes electrons from the valence band of a semiconductor photocatalyst to its conduction band, generating electrons and holes. Density functional theory is widely used for investigating the properties of defects in bulk and on the surface of solids. However, Local or semi-local approximations in the density functional may cause incorrect occupation of defect states and incorrect formation energies. These methods also underestimate the localization of defect states, missing the formation of small polarons. I show that, by making the atom- and angular-momentum-dependent parameters of the Lany-Zunger polaron correction also coordination-dependent, it is possible to correctly describe charge trapping in small polaron states on the anatase (101) and rutile (110) surfaces at a low computational cost. I implemented Komsa and Pasquarello correction scheme for charged models in a user-friendly code and extended the method to handle mediums with anisotropic dielectric tensors as well as cases where the extra charge is localized at multiple sites. In slab models with a large vacuum between the layers, a posteriori charge correction methods may not be adequate, and self-consistent correction may be needed to eliminate the spurious effects. I introduce a self-consistent potential correction method, co-developed by myself, that is capable of dealing with those cases. Finally, I use the developed framework to investigate the photocatalytic CO oxidation on the anatase (101) surface. For the restoration of the pristine surface, I propose a mechanism to eliminate the surface oxygen vacancies by including electron-scavenging oxygen molecules in the gas phase. With the proposed mechanism, it is possible to achieve a complete catalytic cycle for the oxidation of CO over the anatase (101) surface.