First-Principles Approach for Energy Level Alignment at Aqueous Semiconductor Interfaces

A first-principles approach is demonstrated to calculate the relationship between aqueous semiconductor interface structure and energy level alignment. The physical interface structure is sampled using density functional theory based molecular dynamics, yielding the interface electrostatic dipole. The $GW$ approach is used to place the electronic band edge energies of the semiconductor relative to the occupied $1b_1$ energy level in water. Application to the specific cases of non-polar $(10\bar{1}0)$ facets of GaN and ZnO reveals a significant role for the structural motifs at the interface, including the degree of interface water dissociation and the dynamical fluctuations in the interface Zn-O and O-H bond orientations. These effects contribute up to 0.5 eV.