The vibrational properties of strongly coupled one-dimensional electron-lattice systems are dis-tinct form those of weakly coupled ones. While the weakly coupled systems have only four localized modes around the soliton and there is overlap between acoustic and optical phonon branches, the strongly coupled systems can possess more localized modes, and no overlap exists. In terms of the coupling constant λ, the boundary beween strong and weak coupling is λe=0.2119. The number of localized modes depends on λ, and each localized mode can only exist for a certain region of λ. Then the whole rane [0.2/π] of λ can be divided into seven regions, each of which has a charac-teristic disposition of the localized modes.

On the basis of a model similar to that of Su, Schrieffer, and Heeger, we investigate transitions be-tween bipolaron and polaron states In doped heterOCyCle polymers such as polypyrrole, polythlophene, and polyselenophene. The dopant impurity is assumed to be located between chains, and the interchain oupling is due to the electron hopping which is assumed to be confined to nearest-neighboring carbon groups around the counterion. The electron-electron interaction described by a Hubbard-type Hamil-tonian is also included in our calculation. It is shown that the system may be in a bipolaron state or a state of polaron pair of triplet triplet (singlet) nature. We find：that the interchain couping has litthstate of a polaron pair of spin triplet singlet nature We find that the interchain coupling has little influence on the stability of a bipolaron. Transitions from a bipolaron to a pair of polarons can be in-duced 0y a strong electron-electron Interactmn. WnlCn IS also responsible tor the energy dlfierence be-tween the singlet and triplet polarons states.

The ground and excited state energies of the two-dimensional D−centre have been calculated, respectively, as a function of magnetic field. The critical magnetic field values at which the excited states change from unbound to bound have been found. The optical transition between two bound states is discussed. Numerical results with the hyperspherical approach are in good agreement with those obtained through other intensive numerical methods and those obtained through experiments.

The stabilities of solitons, polarons and bipolmns in divalent-doped frompolyacerylene have been shldied by considering the impurity Coulomb confinement as well as the eleetron-electron interactions in the framework of the tight-binding PeierlsHubbard model. It was found that transitions between bipolarons and solitons and between bipolarons and polarons will rake place under cert3in conditions. The calculated values of the energy msitions agree well with the experimental results in the dilute Ca2+-doped trans-polyaceiylene material. The stability of excitations with respect to the impurity confinement and the electron4edron interactions have been discussed.

Spin-polarized current through a ferromagnetic/organic interface was studied theoretically. This study was stimulated by recent experiments on La1−xSrxMnO3 /Alq3/Co and La1−xSrxMnO3/sexithienyl/La1−xSrxMnO3 structures. According to the spin-diffusion equation, the current spin polarization was obtained by assuming that spin polarons as well as spinless bipolarons to be the carriers in the organic semiconductor. It was found that polarons are the effective spin carriers of a spin-polarized current, even though they constitute only a fraction of all carriers. Effects of interfacial electrochemical-potential difference and conductivity matching on spin polarization of the current are discussed.