Modeling Electronic Trap States at Interfaces between Anatase Nanoparticles

Interfaces between crystallites in nanocrystalline anatase can give rise to localized electronic trap states, which affect the charge transport and catalytic activity of mesoporous TiO2 films and aerogels. Unlike trap states associated with point defects and surfaces, the energetic and spatial distributions of interfacial trap states are not known. We have calculated the electronic structure of attached anatase nanoparticles to search for molecular orbitals localized at the particle interfaces and to identify their energetic positions in the nominal band gap. We found that orbitals localized at the interfaces had energies near the edge of the nominal conduction band and that such trap states localized at the interface between (001) facets were lower in energy than those localized at the interface between (101) facets. The spatial distributions of the interfacial trap states were similar between different levels of theory; however, hybrid density functional theory (DFT) predicted the trap states to be deeper than those predicted by DFT within the generalized gradient approximation or by density functional tight binding (DFTB).