  Employing the $G_0W_0$ approximation of Hedin's $GW$ approach one can obtain
quasi-particle energies of extended systems and molecules with good accuracy.
However, for many materials, semi-local exchange-correlation functionals are
unsatisfactory starting points for $G_0W_0$ calculations. Hybrid functionals
often improve upon them, but at a substantially higher computational cost. As
an alternative, we suggest the LDA-1/2 method, which provides reasonable band
gaps, without being computationally involved. In this work, we systematically
compare 3 starting points for $G_0W_0$: LDA, PBE0, and LDA-1/2. A selection of
solids is chosen for this benchmark: C, Si, SiC, AlP, LiF, MgO, Ne, Ar, GaN,
GaAs, CdS, ZnS, and ZnO. We demonstrate that LDA-1/2 is a good starting point
in most cases, reducing the mean absolute error of band gaps by 50% when
compared to the other 2 functionals.
