Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.
Institute of Physics, University of Brasília, 70.919-970 Brasília, Brazil.
J Chem Phys. 2017 Apr 14;146(14):144903. doi: 10.1063/1.4979950.
The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations. These critical electric fields are considerably smaller for inorganic lattices in comparison to organic polymers. Interestingly, for inorganic lattices, the free electron propagates preserving charge and spin densities' localization which is a characteristic of a static polaron. Moreover, in the turning points of the spatial Bloch oscillations, transient polaron levels are formed inside the band gap, thus generating a fully characterized polaron structure. For the organic case, on the other hand, no polaron signature is observed: neither in the shape of the distortion-those polaron profile signatures are absent-nor in the energy levels-as no such polaron levels are formed during the simulation. These results solve controversial aspects concerning Bloch oscillations recently reported in the literature and may enlighten the understanding about the charge transport mechanism in polymers above their mobility edge.
在包括晶格弛豫在内的一维紧束缚模型框架内，理论上研究了极性子在有机和无机聚合物中超过迁移率阈值的输运。该计算方法基于参数，模型哈密顿量适用于存在外电场时不同聚合物晶格的描述。我们的研究结果表明，在临界场强以上，离域的极化子作为自由电子在聚合物晶格中移动，产生 Bloch 振荡。与有机聚合物相比，无机晶格的这些临界电场强度要小得多。有趣的是，对于无机晶格，自由电子在传播过程中保持电荷和自旋密度的局域性，这是静态极化子的特征。此外，在空间 Bloch 振荡的转折点处，带隙内会形成瞬态极化子能级，从而产生完全特征化的极化子结构。另一方面，对于有机情况，没有观察到极化子的特征：无论是在畸变的形状上——这些极化子轮廓特征不存在——还是在能级上——因为在模拟过程中没有形成这样的极化子能级。这些结果解决了文献中最近报道的有关 Bloch 振荡的争议性问题，并可能有助于理解聚合物在迁移率边缘以上的电荷输运机制。
