The Role of Long-Range Coulomb Interaction in theNeutral-to-Ionic Transition of Quasi-One-Dimensional Charge TransferCompounds

Abstract

The neutral (N)-to-ionic (I) transition with dimerization, found inorganic charge transfer compounds with mixed stacking, has beenstudied using a self-consistent theory which takes exact account oflong-range Coulomb interactions but neglects interchain coupling.The unrestricted Hartree-Fock approximation gives a set of optimallymixed donor-acceptor bands with optical gap which bifurcatesin the I phase.The dimerization is ascribed to the electrostatic instability, ratherthan to the distance dependence of the intermolecular electronic transferenergy as is usually done.The phase diagram for the first-order N-I transition with dimerizationand discontinuous change of charge transfer is presented on theparameter plane of the redox potential and the transfer energy.The results of numerical calculations are consistent with the experimental data for tetrathiafulvalene-chloranil compound.