Moiré excitons with Wannier functions

Recent studies in moiré superlattices have demonstrated that many properties of excitons, such as their localization, and lifetimes can be controllably manipulated. Existing theoretical strategies to model moiré excitons, such as those based on effective mass models, neglect several important aspects including atomic reconstructions that take place in a moiré superlattice. On the other hand, the highly accurate first-principles GW-plus-Bethe-Salpeter-Equation (GW+BSE) approach is computationally much more demanding. To make these calculations affordable without compromising accuracy, we develop a new framework to solve the BSE using density-functional-theory calculations in conjunction with Wannier functions. We use the Keldysh potential to describe the screened Coulomb interaction with the parameters obtained from first-principles calculations. Our calculations accurately predict the A and B excitons in semiconducting monolayer transition-metal-dichalcogenides at a fraction of the conventional GW+BSE computational cost. Motivated by recent experiments, we study the twist-angle dependence of the low-energy intralayer and interlayer moiré excitons of the WS2/WSe2 heterobilayer. Our calculations are in good agreement with previous studies.