  The need to interpret ultraviolet photoemission data strongly motivates the
refinement of first-principles techniques able to accurately predict spectral
properties. In this work we employ Koopmans-compliant functionals, constructed
to enforce piecewise linearity in approximate density functionals, to calculate
the structural and electronic properties of DNA and RNA nucleobases. Our
results show that not only ionization potentials and electron affinities are
accurately predicted with mean absolute errors < 0.1 eV, but also that
calculated photoemission spectra are in excellent agreement with experimental
ultraviolet photoemission spectra. In particular, the role and contribution of
different tautomers to the photoemission spectra are highlighted and discussed
in detail. The structural properties of nucleobases are also investigated,
showing an improved description with respect to local and semilocal
density-functional theory. Methodologically, our results further consolidate
the role of Koopmans-compliant functionals in providing, through
orbital-density-dependent potentials, accurate electronic and spectral
properties.
