Spectral Analysis Of Polaron Dynamics In Conjugated Polymers

To understand the dynamic properties of polaron in conjugated polymers, we have investigated various spectra of electric current density, charge density, and lattice vibrations of acoustic and optic modes based on the Su-Schrieffer-Heeger model, by using nonadiabatic molecular dynamics and power-spectrum density methods. A series of characteristic peaks have been identified. In the spectrum of current density, besides the fact that the amplitude of the zero-frequency peak corresponds to the average velocity of the polaron as expected, it is also found that the fundamental frequency is proportional to the polaron velocity. Furthermore, in the case of low electric field strength, the spectra of charge density and acoustic and optic modes present a similar structure as that of the current density, which implies the charge is coupled with both acoustic and optic modes, and the polaron moves at a slightly lower velocity than the speed of the phonon. However, when the electric field increases beyond a critical value, the fundamental frequencies of charge density and optic mode are the same as that of the current density, about 3 times that of acoustic mode, while the fundamental frequency of acoustic mode basically remains constant, the polaron moves at a supersonic speed. Additionally, a characteristic peak corresponding to the breather has been observed mainly in the spectrum of optic mode. Furthermore, the effects of electron-electron interactions on the weight of the breather characteristic peak are briefly discussed.