  In this work we present a new procedure to compute optical spectra including
excitonic effects and approximated quasiparticle corrections with reduced
computational effort. The excitonic effects on optical spectra are included by
solving the Bethe-Salpeter equation, considering quasiparticle eigenenergies
and respective wavefunctions obtained within DFT-1/2 method. The electron-hole
ladder diagrams are approximated by the screened exchange. To prove the
capability of the procedure, we compare the calculated imaginary part of the
dielectric functions of Si, Ge, GaAs, GaP, GaSb, InAs, InP, and InSb with
experimental data. The energy position of the absorption peaks are correctly
described. The good agreement with experimental results together with the very
significant reduction of computational effort makes the procedure suitable on
the investigation of optical spectra of more complex systems.
