Electron localization and the transition from adiabatic to nonadiabatic charge transport in organic conductors.

This tutorial review describes an atomistic simulation approach to studies of dynamics of charge transport in pi-conjugated molecular or polymer based materials. The approach, which is termed electron-lattice dynamics, is based on the Ehrenfest theorem and includes nonadiabatic transport processes. The equations of motion for both the electrons and the nuclei are solved simultaneously using a Runge-Kutta method. We show that for ideal systems without disorder and thermal fluctuations in the electronic coupling between the constituent elements that the electron transport can be described as an adiabatic polaron drift process. In the presence of thermal fluctuations caused by, e.g., phenyl ring torsions along a poly(paraphenylene vinylene) chain, there are extensive variations in the electronic coupling along the polymer chain which results in nonadiabatic hopping transport.