  The LDA-1/2 method has proven to be a viable approach for calculating band
gaps of semiconductors. To address its accuracy for finite systems, we apply
LDA-1/2 to atoms and the molecules of the $GW100$ test set. The obtained
energies of the highest-occupied molecular orbitals are validated against
CCSD(T) data and the $G_0W_0$ approach of many-body perturbation theory. The
accuracy of LDA-1/2 and $G_0W_0$ is found to be the same, where the latter is
computationally much more involved. To get insight into the benefits and
limitations of the LDA-1/2 method, we analyze the impact of each assumption
made in deriving the methodology.
