On the structure of bipolaronic defects in thiophene oligomers: a density functional study

The neutral and dication species of thiophene oligomers of increasing size (2 to 12 rings) have been examined and a study made of structural modifications occurring due to the increase in molecular charge; molecular properties such as charge-density distribution have been calculated. Preliminary results concerning the effect of electron correlation included at the density functional theory level are reported. Significant differences with respect to Hartree-Fock results are observed: the whole bipolaronic defect shape changes so that in the longer oligomers the bond-length alternation is no longer present.