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).