Localized modes of lattice vibration in polythiophene are investigated numerically by considering a chain of finite length. th the periodic boundary condition, we find three even-parity and four odd-parity modes. One of the even modes due to the sulfur heteroatom in the heterocycle is believed to be re-sponsible for what is observed around 700 cm. in the Raman spectrum of polythiophene. With the free-end boundary condition, several modes from the highest optical branch become localized near the surface. These modes may be identified as the high-frequency modes observed in infrared-active vibra-tion and resonant. Raman. scattering absorption experiments.

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 electrical transport of DNA is closely related to the density of itinerant π electrons because of the strong electron-lattice interaction. The resistivities of two typical DNA molecules [poly(dG)-poly(dC) and λ-DNA] with varied densities of itinerant π electrons are calculated. It is found that the dependence of the resistivity on the density of itinerantπelectrons is symmetrical about the half-filling state of itinerant π electrons in poly(dG)-poly(dC). At the half-filling state, the Peierls phase transition takes place and poly(dG)-poly(dC) has a large resistivity. When the density of itinerant π electrons departs far from the half-filling state, the resistivity of poly(dG)-poly(9dC) becomes small. Forλ-DNA, there is no Peierls phase transition due to the aperiodicity of its base pair arrangement. The resistivity of poly(dG)-poly(dC) decreases with increasing length of the molecular chain, but the resistivity of λ-DNA increases with increasing length. The conducting mechanisms for poly(dG)-poly(dC) and a few λ-DNA molecules with varied densities of itinerantπelectrons are analyzed.

Instead of spin electrons or holes, the carriers in polymers are supposed to be spin polarons or spinless bipolarons. Based on the spin diffusion theory and Ohm's law, we studied spin-polarized injection into organic polymers. It was obtained that only spin polarons are responsible for the current spin polarization in a ferromagnetic (FM)/organic system. Effects of the conductivity matching and the interfacial resistances on the current spin polarization were discussed.

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.