Spectral analysis of bipolaron dynamics in nondegenerate conjugated polymers

Abstract

Spectral characteristics of the bipolaron dynamics in nondegenerate polymers have been investigated based on the Su-Schrieffer-Heeger model, by using nonadiabatic molecular dynamics and power-spectrum density methods. The results show that the fundamental frequencies of bond-current density are proportional to the saturation velocities of the bipolaron. Further, the dependence of the fundamental frequencies of bond-current density on electric field and temperature can be divided into two cases. For the case of the field higher than a critical value, the thermal effects enhance the fundamental frequency of bond-current density, whereas at field lower than the threshold, the fundamental frequency is inhibited by thermal effects. It reflects the competition between electric field and temperature in bipolaron dynamics. Moreover, in the spectrum of optic mode, the weight of characteristic peak corresponding to breather first rapidly increases and then increases slowly with increasing electric field, which corresponds to the variation of the bipolaron velocity.