  The $GW$ approximation has become an important tool for predicting charged
excitations of isolated molecules and condensed systems. Its popularity can be
attributed to many factors, including a favorable scaling and relatively good
accuracy. In practical applications, the $GW$ is often performed as a one-shot
perturbation known as $G_0W_0$. Unfortunately, $G_0W_0$ suffers from a strong
starting point dependence and is often not as accurate as one would need.
Self-consistent $GW$ methodologies alleviate these problems but come with a
marked increase in computational cost. In this manuscript, we propose the use
of an estimate of the exchange-correlation derivative discontinuity to provide
a remarkably good starting point for $G_0W_0$ calculations, yielding ionization
potentials and electron affinities with eigenvalue self-consistent $GW$ quality
at no additional cost. We assess the quality of the resulting methodology with
the GW100 benchmark set and compare its advantages over other similar methods.
