  We use first-principles computational methods to examine hole trapping in
organic molecular crystals. We present a computational scheme based on the
tuning of the fraction of exact exchange in hybrid density functional theory to
eliminate the many-electron self-interaction error. With small organic
molecules, we show that this scheme gives accurate descriptions of ionization
and dimer dissociation. We demonstrate that the excess hole in perfect
molecular crystals form self-trapped molecular polarons. The predicted absolute
ionization potentials of both localized and delocalized holes are consistent
with experimental values.
