Ab Initio Positioning of the Valence and Conduction Bands of Bulk Photocatalysts: Proposition of Absolute Reference Energy

Finding absolute reference energy from first-principles calculations to align redox positions of valence band top and hence conduction band bottom of bulk inorganic photocatalysts is still a challenge. A theoretical methodology is proposed herein based on first-principles calculations using the state-of-the-art hybrid density functional theory from Heyd-Scuseria-Ernzerhof. Both oxide and nonoxide materials, known for their potential capability for photocatalysis, i.e., rutile and anatase TiO2; wurtzite ZnO; rutile SnO2; and the blende phase of GaP, GaAs, InP, ZnTe, CdS, CdSe, and SiC, have been studied. The calculated band edges around the fundamental band gap of these compounds are realigned, in reference to the corrected vacuum energy level from the probe's core energy state, i.e., the 1s(2) state of an unreactive helium atom. The calculated ab initio positioning of valence and conduction band extrema is compared to the available experimental data, and our prediction is best fitted within a mean absolute error of 0.2 eV.