Heterogeneous photocatalysis is a promising approach to solving a range of chemical problems in a sustainable way, directly converting energy from radiation (e.g. sunlight) into the driving force for chemical reactions. Potential large scale applications span from producing energetic or high value products like hydrogen gas to destroying problematic pollutants like PFAS. Photocatalytic materials generally rely on the separation of photo-generated electrons and holes, often through "band bending" at interfaces. Studying band bending has traditionally been the preserve of condensed matter physics using continuum approaches to evaluating Fermi level alignment, etc. In this talk I will discuss how one can examine band bending explicitly in atomistic simulations based on density functional theory, revealing the effect of atomic reconstruction at interfaces, charge transfer, interface states, etc.