Bulk ionization potentials and band alignments from three-dimensional periodic calculations as demonstrated on rocksalt oxides

The position of the band edges of a material plays a key role in determining the properties for a range of applications, but fundamental band bending is an interface-dependent property that cannot be quantified without knowledge of bulk electron energy levels. We present a method for calculating the bulk position of the valence band maximum, and therefore the bulk ionization potential, from periodic plane wave calculations as shown for a range of rocksalt ionic oxides. We demonstrate that, for the popular "slab alignment" technique, explicit consideration of any surface induced electronic polarization is necessary to calculate accurate bulk ionization potentials. Our proposed method to quantify these surface effects, using polarizable-shell based interatomic potentials, is very computationally affordable, and our updated slab alignment method yields much improved agreement with the available experimental data.