Shakiba Mohammad, Stippell Elizabeth, Li Wei, Akimov Alexey V
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States.
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
J Chem Theory Comput. 2022 Sep 13;18(9):5157-5180. doi: 10.1021/acs.jctc.2c00297. Epub 2022 Jun 27.
In this work, we report a new methodology for nonadiabatic molecular dynamics calculations within the extended tight-binding (xTB) framework. We demonstrate the applicability of the developed approach to finite and periodic systems with thousands of atoms by modeling "hot" electron relaxation dynamics in silicon nanocrystals and electron-hole recombination in both a graphitic carbon nitride monolayer and a titanium-based metal-organic framework (MOF). This work reports the nonadiabatic dynamic simulations in the largest Si nanocrystals studied so far by the xTB framework, with diameters up to 3.5 nm. For silicon nanocrystals, we find a non-monotonic dependence of "hot" electron relaxation rates on the nanocrystal size, in agreement with available experimental reports. We rationalize this relationship by a combination of decreasing nonadiabatic couplings related to system size and the increase of available coherent transfer pathways in systems with higher densities of states. We emphasize the importance of proper treatment of coherences for obtaining such non-monotonic dependences. We characterize the electron-hole recombination dynamics in the graphitic carbon nitride monolayer and the Ti-containing MOF. We demonstrate the importance of spin-adaptation and proper sampling of surface hopping trajectories in modeling such processes. We also assess several trajectory surface hopping schemes and highlight their distinct qualitative behavior in modeling the excited-state dynamics in superexchange-like models depending on how they handle coherences between nearly parallel states.
在这项工作中，我们报告了一种在扩展紧束缚（xTB）框架内进行非绝热分子动力学计算的新方法。通过对硅纳米晶体中的“热”电子弛豫动力学以及石墨相氮化碳单层和钛基金属有机框架（MOF）中的电子 - 空穴复合进行建模，我们证明了所开发方法对包含数千个原子的有限和周期性系统的适用性。这项工作报道了迄今为止xTB框架所研究的最大直径达3.5 nm的硅纳米晶体中的非绝热动力学模拟。对于硅纳米晶体，我们发现“热”电子弛豫速率对纳米晶体尺寸呈非单调依赖性，这与现有实验报告一致。我们通过与系统尺寸相关的非绝热耦合的降低以及具有更高态密度的系统中可用相干转移途径的增加的组合来解释这种关系。我们强调正确处理相干性对于获得这种非单调依赖性的重要性。我们对石墨相氮化碳单层和含钛MOF中的电子 - 空穴复合动力学进行了表征。我们证明了自旋适配和表面跳跃轨迹的适当采样在模拟此类过程中的重要性。我们还评估了几种轨迹表面跳跃方案，并突出了它们在模拟类超交换模型中的激发态动力学时根据处理近平行态之间相干性的方式而表现出的不同定性行为。
