First-principles quantum and quantum-classical simulations of exciton diffusion in semiconducting polymer chains at finite temperature.
First-principles quantum and quantum-classical simulations of exciton diffusion in semiconducting polymer chains at finite temperature.
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DOI：
10.1021/acs.jctc.0c00351
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发表时间：
2020-07
影响因子：
5.5
通讯作者：
R. Hegger;R. Binder;I. Burghardt
中科院分区：
文献类型：
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作者：
R. Hegger;R. Binder;I. Burghardt
我们报告的第一性原理量子动力学和量子经典模拟的光致激子动力学在寡聚噻吩链段，代表链内激子迁移的聚（3-hexylthiophene）（P3 HT）聚合物。跟进我们最近的研究[宾德和伯格哈特，法拉第讨论。221，406（2020）]，对包含20个单体单元（OT-20）的短寡聚噻吩链段进行多层多构型时间依赖哈特里（ML-MCTDH）计算，以获得有限温度下的完整量子动力学模拟。这些都是基准平均场Eklfest计算，这是给本系统的定性正确的结果。周期性的边界条件，显着改善早期的估计扩散系数。使用Eschlafest方法，随后进行了一系列的计算较大的晶格（OT-40至OT-80），导致温度依赖的均方位移，这被发现表现出近线性的依赖性作为时间的函数的估计。由此产生的扩散系数估计是温度的递增函数，其详细的函数形式取决于静态无序的程度。在实际的静态无序方差（σs ≤ 0.06 eV）下，扩散系数从D ~ 1 × 10-2 cm ~ 2s ~（-1）下降到D ~ 1 × 10-3 cm ~ 2s ~（-1），与P3 HT的实验数据定性一致。从我们的模拟获得的动力学方案表明，在P3 HT型链中的激子迁移在我们研究的整个温度范围内是一个很大程度上绝热的过程（即，T = 50 K至T = 300 K）。由此产生的激子迁移的图片是一个相干的，但不是带状的，激子极化子的运动所引起的波动低频模式驱动。如果静态无序变得突出并且安德森局域化开始，则该过程获得部分跳跃特征。
We report on first-principles quantum-dynamical and quantum-classical simulations of photoinduced exciton dynamics in oligothiophene chain segments, representative of intra-chain exciton migration in the poly(3-hexylthiophene) (P3HT) polymer. Following up on our recent study [Binder and Burghardt, Faraday Discuss. 221, 406 (2020)], Multi-Layer Multiconfiguration Time-Dependent Hartree (ML-MCTDH) 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 variance (σs ≅ 0.06 eV), the diffusion coefficients decrease from D ~ 1 x 10-2 cm2s-1 to D ~ 1 x 10-3 cm2s-1, 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., T = 50 K to T = 300 K). The resulting picture of exciton migration is a coherent, but not band-like, 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.