Effective Residual Interaction Kernel Approach for Optical Spectra

Excitonic effects dominate absorption and loss spectra in many materials. However, they are hard to access computationally, because of the cost of first-principles calculations and because of the scarce reliability of simple approximations. We overcome both limitations by combining a part of the electron-hole Bethe-Salpeter equation with an effective scalar interaction. The partitioning is motivated by the general form of the electron-hole interaction and it can be applied to all materials. First-principles calculations for prototypical semiconductors and insulators demonstrate a speedup of 1 to 2 orders of magnitude for results close to those where the full interaction matrix is used. The method is systematic and can be converged to the benchmark.