Computational exploration of previously unknown reactive sites is a powerful strategy for 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 considers 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 β-Ga2O3 and θ-Al2O3. Seven and six terminations considered experimentally accessible are found for β-Ga2O3 and θ-Al2O3, respectively, where the highest surface energy was roughly twice of the lowest. The lowest surface O vacancy formation energy (EOvac) in an accessible surface is 3.04 and 5.46 eV in the ( 101) and ( 201 ) terminations for β-Ga2O3 and θ-Al2O3, respectively, where the decrease in EOvac from the most stable surface is 1.32 and 1.11 eV, respectively. The EOvac in accessible surfaces showed a good correlation with 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.
Metal/oxide
support perimeter sites can provide unique properties
because the local environment on the support surface is changed by
the nearby metal. This study modeled perimeter sites when metal nanorods
were adsorbed in lieu of nanoparticles on the (111) surface of an
In2O3 support. The metal element M was one of
Ag, Au, Cu, Ir, Pd, Pt, and Re. Changes in the surface oxygen vacancy
formation energy (E
Ovac) with nanorod
adsorption were evaluated using systematic first-principles calculations
under the same approximations and conditions and were found to be
driven by two major factors. First, if the Fermi energy of the metal
is deeper than the defect energy level of surface O vacancies, the
metal may act as an electron scavenger to accept excess electrons
upon O removal from sites close to the metal. The minimum E
Ovac for each M correlated very well with the
Bader charge transfer to the nanorod upon O removal. The effect of
geometrical relaxation of the nanorod after O removal was not found
because there was barely any spontaneous rearrangement of nanorod
atoms after O removal. As a consequence, the minimum E
Ovac in a surface tends to decrease with the increasing
work function of M. Second, among different O sites on the same surface, E
Ovac is lower in O sites when there are interface
states with the adsorbed metal at energy levels higher than the valence
band of the support. These insights would help in planning strategies
to obtain active O sites.
Screening of surfaces that spontaneously reconstruct is important when investigating realistic surfaces. Evaluating the surface energy after macroscopic reconstruction to form pairs of facets is a very fast procedure to identify surfaces that spontaneously reconstruct. This paper discusses a method to identify orientations of pairs of facets that can form on an arbitrary crystal orientation, which can then be used to derive the surface energy after facet reconstruction. Another use of the algorithm is to find possible orientations of terrace surfaces when the vicinal surface orientation is known for a surface with step edges. The algorithm is expected to further accelerate high-throughput calculations of surface properties.
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