  The exciton binding energy, the energy required to dissociate an excited
electron-hole pair into free charge carriers, is one of the key factors to the
optoelectronic performance of organic materials. However, it remains unclear
whether modern quantum-mechanical calculations, mostly based on Kohn-Sham
density functional theory (KS-DFT) and time-dependent density functional theory
(TDDFT), are reliably accurate for exciton binding energies. In this study, the
exciton binding energies and related optoelectronic properties (e.g., the
ionization potentials, electron affinities, fundamental gaps, and optical gaps)
of 121 small- to medium-sized molecules are calculated using KS-DFT and TDDFT
with various density functionals. Our KS-DFT and TDDFT results are compared
with those calculated using highly accurate CCSD and EOM-CCSD methods,
respectively. The omegaB97, omegaB97X, and omegaB97X-D functionals are shown to
generally outperform (with a mean absolute error of 0.36 eV) other functionals
for the properties investigated.
