Hegger Rainer, Binder Robert, Burghardt Irene
Institute for Physical and Theoretical Chemistry, Goethe University, Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany.
J Chem Theory Comput. 2020 Sep 8;16(9):5441-5455. doi: 10.1021/acs.jctc.0c00351. Epub 2020 Aug 20.
We report on first-principles quantum-dynamical and quantum-classical simulations of photoinduced exciton dynamics in oligothiophene chain segments, representative of intrachain exciton migration in the poly(3-hexylthiophene) (P3HT) polymer. Following up on our recent study (Binder R.; Burghardt, I. , , 406), multilayer multiconfiguration time-dependent Hartree calculations for a short oligothiophene segment comprising 20 monomer units (OT-20) are carried out to obtain full quantum-dynamical simulations at finite temperature. These are employed to benchmark mean-field Ehrenfest calculations, which are shown to give qualitatively correct results for the present system. Periodic boundary conditions turn out to significantly improve earlier estimates of diffusion coefficients. Using the Ehrenfest approach, a series of calculations are subsequently carried out for larger lattices (OT-40 to OT-80), leading to estimates for temperature-dependent mean-squared displacements, which are found to exhibit a near-linear dependence as a function of time. The resulting diffusion coefficient estimates are an increasing function of temperature, whose detailed functional form depends on the degree of static disorder. With a realistic static disorder parameter (σ ≃ 0.06 eV), the diffusion coefficients decrease from ∼ 1 × 10 cm s to ∼ 1 × 10 cm s, in qualitative agreement with experimental data for P3HT. The dynamical scenario obtained from our simulations shows that exciton migration in P3HT-type chains is a largely adiabatic process throughout the temperature regime we investigated (i.e., = 50-300 K). The resulting picture of exciton migration is a coherent, but not bandlike, motion of an exciton-polaron driven by fluctuations induced by low-frequency modes. This process acquires partial hopping character if static disorder becomes prominent and Anderson localization sets in.
我们报道了对低聚噻吩链段中光致激子动力学的第一性原理量子动力学和量子经典模拟，该链段是聚（3-己基噻吩）（P3HT）聚合物中链内激子迁移的代表。继我们最近的研究（Binder R.；Burghardt, I. ， ，406）之后，对包含20个单体单元的短低聚噻吩链段（OT-20）进行了多层多组态含时Hartree计算，以获得有限温度下的全量子动力学模拟。这些模拟被用于检验平均场埃伦费斯特计算，结果表明该计算对当前系统给出了定性正确的结果。事实证明，周期性边界条件能显著改进扩散系数的早期估计。使用埃伦费斯特方法，随后对更大的晶格（OT-40至OT-80）进行了一系列计算，得出了与温度相关的均方位移估计值，发现其随时间呈现近似线性关系。由此得到的扩散系数估计值是温度的增函数，其详细的函数形式取决于静态无序程度。采用实际的静态无序参数（σ≃0.06 eV）时，扩散系数从～1×10 cm²/s降至～1×10 cm²/s，与P3HT的实验数据定性一致。我们模拟得到的动力学情景表明，在我们研究的整个温度范围（即T = 50 - 300 K）内，P3HT型链中的激子迁移在很大程度上是一个绝热过程。由此得到的激子迁移图景是由低频模式诱导的涨落驱动的激子 - 极化子的相干但非带状运动。如果静态无序变得显著且出现安德森局域化，这个过程就会具有部分跳跃特征。
