Finite-momentum dielectric function and excitonic effects from time-dependent density-functional theory with dielectrically screened hybrid functionals

Abstract: This paper studies the performance of time-dependent density-functional theory (TDDFT) for calculating the dielectric function of semiconductors and insulators at finite momentum transfer, comparing against the standard Bethe-Salpeter equation (BSE). Specifically, we consider a recently proposed hybrid approach that mixes dielectrically screened exact exchange with a semilocal functional, and we also introduce a new hybrid functional featuring a truncated dielectric screening scheme. The computational effort of these hybrid TDDFT approaches is significantly less than that of the BSE, but they deliver comparable accuracy, as demonstrated for the semiconductors Si and GaN and the wide-band insulator LiF. This opens up possibilities for calculating exciton dispersions and electron energy loss functions efficiently and accurately for a wide range of materials.