Aligning electronic energy levels at the TiO2/H2O interface

The electronic energy levels of a model titanium dioxide water interface computed using the Perdew-Burke-Ernzerhof (PBE) density functional are positioned relative to the normal hydrogen electrode and vacuum. As energy reference we use the solvation free energy of the H+ ion computed by reversible insertion of a proton in the aqueous part of the model system. The interaction with water raises the energy levels bringing the conduction-band edge in fair alignment with experiment. The error in the PBE band gap must therefore be largely attributed to underestimation of the ionization potential.