First-principles calculations of functionalized TᵢO₂ rutile (110) surface
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Abstract
Titanium dioxide (TiO2) is widely used in photocatalysis due to its chemical stability in air and water, non-toxicity, low cost, and band-edge positions that enable oxidative and reductive reactions under UV illumination. Among its low-index facets, the rutile TiO2(110) surface is the thermodynamically most stable and therefore has the lowest surface energy compared to other facets. Its characteristic arrangement of undercoordinated titanium and oxygen atoms at the surface provides sites for the adsorption of water and organic molecules providing a relationship between surface structure and photocatalytic function. Electronic and surface properties of the TiO2 rutile (110) surface were studied using Density Functional Theory (DFT) with the PBE functional. A well-known limitation of semilocal DFT with the PBE functional is severe underestimation of the bandgap, arising from self-interaction errors and the absence of non-local exchange, which leads to overly delocalized Ti 3d states and an incorrect separation between valence and conduction bands. To obtain a more accurate description of the surface electronic structure, a Hubbard U correction was applied to the Ti 3d orbitals (DFT+U), partially correcting the self-interaction error and improving the predicted bandgap. Rutile (110) slab models were constructed and converged in slab thickness with respect to surface energy and electronic bandgap to have a more accurate description of the surface properties. On this electronically converged rutile (110) slab, the adsorption of water and methanol is investigated. Preferred adsorption configurations and adsorption energies are characterized, and the resulting modifications to the surface electronic structure are analyzed through band-structure and density of states calculations. The findings clarify how molecular adsorption on TiO2(110) shifts band edges and alters surface states, thereby tuning the photocatalytic behavior of the Rutile (110) surface.
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2026