Ab-initio study of singlet and triplet excitation energies in oligothiophenes

We report singlet and triplet electronic excitations in oligomers of thiophene using a state-of-art ab-initio approach, i.e. the approximated coupled cluster singles and doubles method. This highly correlated and size-consistent method is required to correctly describe excitonic effects in such strongly confined systems. We show that this approach provides an excellent accuracy in reproducing absolute values and chain-length evolution of excitation energies as compared with recent photo-detachment photoelectron spectroscopy measurements.