Surface Oxygen Vacancy Formation Energy Calculations in 34 Orientations of β-Ga<sub>2</sub>O<sub>3</sub> and θ-Al<sub>2</sub>O<sub>3</sub>
Yoyo Hinuma, Takashi Kamachi, Nobutsugu Hamamoto, Motoshi Takao, Takashi Toyao, Ken‐ichi Shimizu
Abstract
Computational exploration of previously unknown reactive sites is a powerful strategy for the emergence of new catalytic reactions. Exotic surfaces can be theoretically investigated, but there are very few, if any, computational models of high-index orientations that consider the reconstruction of the surface. A workflow to efficiently obtain a set of accessible terminations by removing those that are metastable against macroscopic facet formation and by comparing cleaved surfaces and surfaces suggested by a genetic algorithm (GA) for promising orientations is proposed and demonstrated using 34 orientations of beta-Ga2O3 and theta-Al2O3. Seven and six terminations considered to be experimentally accessible are found for beta-Ga2O3 and theta-Al2O3, respectively, where the highest surface energy was roughly twice that of the lowest. The lowest surface 0 vacancy formation - energies (E-Ovac) among accessible surfaces are 3.04 and 5.46 eV in the (101) and (20 (1) over bar) terminations for beta-Ga2O3 and theta-Al2O3, respectively, where the decreases in E-Ovac, from the most stable surface are 1.32 and 1.11 eV, respectively. The E-Ovac in accessible surfaces showed a good correlation with the descriptors of the local coordination environment, suggesting that exploiting surface O in an unfavorable environment in an accessible termination would enhance O-vacancy-related catalyst performance even in materials that do not show reactivity on the most stable surface.