Abstract
Summary form only given. The formation of bipolarons and polarons in conjugate polymers with non degenerate ground states is studied theoretically. Our model is the Pariser-Parr Pople model with an electron-lattice interaction of the Su-Schrieffer-Heeger type and with a symmetry-breaking transfer energy modulation (a tight-binding version of the Brazovskii-Kirova model) for a single chain. We investigate systematically the relative stability of a bipolaron and two separated polarons as functions of the Coulomb interaction strength and the transfer modulation within the unrestricted Hartree-Fock approximation. It is demonstrated that Coulomb interaction significantly suppresses the stability of bipolarons. When more carriers are doped in a chain, there is a competition between a polaron lattice and a bipolaron lattice, the latter being stabilized at high doping concentrations. Therefore, our model predicts a possible doping induced transition from a polaron lattice to a bipolaron lattice. We will also discuss the optical properties of bipolarons and polarons.
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