Finite-momentum Dielectric Function And Excitonic Effects From TDDFT With a Dielectrically Screened Hybrid Functional

We study 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. The computational effort of this hybrid TDDFT approach is significantly less than that of the BSE, but it delivers 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.