A comparison of density functional theory (DFT) methods for estimating the singlet-triplet (S0-T1) excitation energies of benzene and polyacenes

► Estimated singlet-triplet excitation energies of linear polyacenes up to decacene. ► Range of density functional theory methods and basis sets employed. ► Significant variability for longer polyacenes dependent on model chemistry. ► B2PLYPD/mPW2PLYPD predict ground state singlets with positive singlet-triplet gaps. ► B2PLYPD predicts vanishingly small singlet-triplet gap at the polymeric limit.