Effective on-site Repulsion in Molecular Conductors with Dimeric Structure: Is the Transfer Integral a Good Measure of Correlation?

The effective repulsive energy between the carriers in a molecular dimer has been examined in terms of the extended Hubbard model. The intermolecular Coulomb repulsion, V , rather than the intradimer transfer integral, t , has been shown to give major contribution to the effective repulsion in a strongly dimerized case. The effective repulsion of the dimer, as well as t , increases upon dimerization, for this reason. This analysis has been applied also to a two-level system, so that the strength of correlation is related to the structural features.