Lithium- and chlorine-doped biphenyl dimers as models for interchain polarons and bipolarons - A density functional study

Charge transfer complexes of lithium and chlorine atoms with biphenyl (BP) dimers have been studied as models for intermolecular polarons and bipolarons by means of density functional calculations. Sandwich-type complexes BP-nX-BP, (X = Li,Cl and n = 1,2), 'top' complexes nX-BP-BP and the charged complexes [BP-BP](n+/-) were considered. Stable dimer structures with stabilization energies ranging from -15 to -71 kcal/mol are found when doping atoms are included. In the case of charged complexes without counterions the interaction energy is only a few kcal/mol. Specific differences in the positions of the doping lithium and chlorine atoms are observed: the lithium atoms are located inside the bilayer formed by the two BP molecules whereas the chlorine atoms are located at the edges.