Adsorption of 2-Vinyl Thiophene on Si(100)2x1: A Van Der Waals Corrected DFT Study

Oligo- and polythiophenes on surfaces play a fundamental role in building molecular circuits and organic-based electronics and may be assembled via interaction of the monomer units with the surface. In this framework, the nature of interaction of 2-vinyl thiophene, a conjugated hetero-aromatic monomer unit, with the Si(100) surface was studies by means of density functional theory (DFT). In particular, structural optimizations were performed comparing the effects of the inclusion of Van der Waals forces. It came out that the adsorption through the double bond is energetically favoured, if Van der Waals forces are included, whereas the adsorption through both aromatic ring and double bond simultaneously is more stable, if they are excluded. Physisorbed states were singled out and the barriers between two of them and the corresponding chemisorbed states were calculated along with the imaginary frequencies of the transition states. Also the transition energies have different values if the Van der Waals forces are included.