Polaron In The Emeraldine-base Polymer Under High Pressure

We report a theoretical study on the geometric and the electronic structure of a polaron in the emeraldine-base polymer under pressure, on the basis of an extended Ginder-Epstein model. Polaron levels were found in the band gap. bond-length and the ring-torsion-angle relaxation involved19sites, form a hole polaron with spin. The spectral absorption of the polaron, consistent with the experimental results. Our theory support the conducting mechanism of polarons in the polymer.Through the numerical simulation of pressure along the direction perpendicular to the chain, we study effects of the pressure at room temperature, which could lead to an increase in conductivity. We found:polaron relaxasion was weaken up to disappear and the original local charge tended to distribute on the whole chain; Because of the pressure excitation energy got lower so that concentration of carriers got higher up to12orders of magnitude. In fact, we met a semiconductor-metal transition, our critic pressure was13.76GPa. Upon the pressure, there were electronic transitions from the top of the valence band to the bottom of the conduction band, theretical peak of absorption was at0.5eV which would be spectrum evidence for the semiconductor-metal transition.Then we made molecular dynamical simulations for mobility of the hole polaron. The results showed that:With the increase of the pressure, the mobility appears to increase after the first reduce the phenomenon, a similar change trend of quadratic function, but always maintain metal-like characteristics, high pressure lead to carrier concentration reached1018cm-3, that made an electrical conductivity of107S·cm-1. The saturated pressure is found at13.76GPa. Our calculated results were consistent with the experimental observasion of the polymer of which conductivity increases with appllying pressure till saturation. The polaron conductive mechanism of polymer was confirmed.