  We used our previously implemented GW approximation (GWA) based on the
all-electron full-potential projector augmented wave (PAW) method to study the
optical properties of small, medium and large-band-gap semiconductors: Si,
GaAs, AlAs, InP, Mg$_2$Si, C, and LiCl. The aim being to study the size of both
local-field (LF) and the quasi-particle (QP) corrections to the calculated
dielectric function obtained using the local density approximation (LDA). We
found that while the QP corrections tend to align the calculated structures in
the optical spectra with their experimental counterparts, the LF effects don't
change these peak positions but systematically reduce the intensities of the so
called $E_1$ and $E_2$ structures in all the optical spectra. The reduction of
the intensity of the $E_1$ peak worsen the agreement with experiment while that
of $E_2$ improves it. We then show that the local-field correction improves
considerably the calculated static dielectric constants of all studied
semiconductors.
  Because the static dielectric constant is a ground state property, the
remaining discrepancy with experiment should be attributed to the the LDA
itself. On the other hand, as expected, the calculation of the static
dielectric constant using the GW quasiparticle energies and including the LF
effects is underestimated for all the semiconductors. The excitonic effects
should then correct for this discrepancy with experiment.
