  Charged excitations of the oligoacene family of molecules, relevant for
astrophysics and technological applications, are widely studied and therefore
provide an excellent system for benchmarking theoretical methods. In this work,
we evaluate the performance of many-body perturbation theory within the GW
approximation relative to new high-quality CCSD(T) reference data for charged
excitations of the acenes. We compare GW calculations with a number of hybrid
density functional theory starting points and with eigenvalue self-consistency.
Special focus is given to elucidating the trend of GW-predicted excitations
with molecule length increasing from benzene to hexacene. We find that GW
calculations with starting points based on an optimally tuned range-separated
hybrid (OTRSH) density functional and eigenvalue self-consistency can yield
quantitative ionization potentials for the acenes. However, for larger acenes,
the predicted electron affinities can deviate considerably from reference
values. Our work paves the way for predictive and cost-effective GW
calculations of charged excitations of molecules and identifies certain
limitations of current GW methods used in practice for larger molecules.
