Vlček Vojtěch, Eisenberg Helen R, Steinle-Neumann Gerd, Neuhauser Daniel, Rabani Eran, Baer Roi
Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth 95440, Germany.
Phys Rev Lett. 2016 May 6;116(18):186401. doi: 10.1103/PhysRevLett.116.186401. Epub 2016 May 2.
Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects, or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally tuned range-separated density functional theory and many-body perturbation calculations within the GW approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies, and the optimally tuned range parameter itself all become independent of polymer length as it exceeds the critical localization length. Moreover, we find that lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.
在扩展原子系统中，电荷载流子的局域化此前被描述为由无序、点缺陷或离子晶格畸变所驱动。在此，我们首次通过第一性原理计算表明，在其他方面完全有序的结构中，电荷载流子可因纯粹的电子效应而自发局域化。在GW近似下的最优调谐范围分离密度泛函理论和多体微扰计算表明，在反式聚乙炔和聚噻吩中，空穴密度在几纳米的长度尺度上局域化。这是由于电荷密度的交换诱导平移对称性破缺。当聚合物长度超过临界局域化长度时，电离势、光吸收峰、激子结合能以及最优调谐范围参数本身都变得与聚合物长度无关。此外，我们发现与传统观点（晶格畸变先于电荷局域化）相反，晶格无序和极化子的形成是由电荷局域化导致的。我们的结果可以解释共轭聚合物中的极化子在暴露于超快光脉冲后瞬间形成的实验发现。
