LITHIUM-DOPED 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 an d bipolarons by means of density functional calculations. Sandwich-typ e complexes BP-nX-BP, (X = Li,Cl and n = 1,2), 'top' complexes nX-BP-B P and the charged complexes [BP-BP](n+/-) were considered. Stable dime r structures with stabilization energies ranging from -15 to -71 kcal/ mol are found when doping atoms are included. In the case of charged c omplexes 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.