Derivative-discontinuity-including functionals for accurate GW-BSE excitation energies

The Bethe-Salpeter equation (BSE) formalism stands as a valuable alternative to time-dependent density functional theory (TD-DFT) for studying the properties of chemical systems of interest for various applications. The BSE equations can be cast in the same Casida formulation as traditional TD-DFT, thus enabling the use of the same tools to solve the equations and permitting the study of systems containing a few hundred atoms. However, calculating the true addition/removal energies using the GW formalism remains the main bottleneck in terms of computer cost, as it is often necessary to perform partial self-consistent GW calculations to obtain accurate optical excitation. By using our recent implementation of the BSE formalism, we will show how the addition of a derivative discontinuity estimate leads to accurate BSE optical excitation spectra using one-shot G₀W₀ addition/removal energies and lowers the overall computational cost by circumventing the need for partial self-consistent GW approaches.