The electronic structure calculations were performed using the Vienna Ab initio Simulation Package (VASP) employing density functional theory (DFT) at the PBE+U level of theory. A plane wave basis set with a cutoff of 600 eV for the bulk and 500 eV for the surface was chosen to represent the valence states. Calculations were performed on a gamma-centered Monkhorst-Pack grid with minimal k-point meshes of (7×7×1), (6×3×1), and (6×6×1) for corundum (+3), rutile (+4) and pentoxide (+5) systems, respectively. Energies were relaxed to a 10 -6 eV convergence threshold, while the forces on each atom were converged to 0.02 eV/Å. Effective Hubbard-U (Ueff) values were applied to the 3d transition metals; the list of values is provided in Table . We have selected the (012) and (100) surfaces for the corundum (+3) and pentoxide (+5) polymorphs, respectively, each with 50% surface coverage. For the rutile (+4) systems, we focused on the (110) surface, employing a high surface coverage. These surface configurations were selected in accordance with our previous research. The projector-augmented wave (PAW) method 28 was used to represent the core electrons.