Towards first-principles based modeling of poly-3-alkylthiophenes: The nature of interactions in 2,2′-bithiophene dimer

In this Letter, we report on the directionality of intermolecular interactions in 2,2′-bithiophene dimer. The decomposition of interaction energy is performed using the density-functional theory-symmetry-adapted perturbation theory. Since in π-conjugated dimers in stacked alignments the dispersion energy is expected to play a crucial role in their stabilization, special attention is paid to this quantity estimated at various levels of theoretical approximation. The primary finding of this study is that a simple exchange-dispersion potential correctly describes the interactions in the studied dimer.