Smith Brendan, Akimov Alexey V
Department of Chemistry , University at Buffalo, The State University of New York , Buffalo , New York 14260 , United States.
J Phys Chem Lett. 2020 Feb 20;11(4):1456-1465. doi: 10.1021/acs.jpclett.9b03687. Epub 2020 Feb 7.
We develop a new express methodology for modeling excited-state dynamics occurring in dense manifolds of electronic states in atomistic systems. The approach leverages a modified Landau-Zener formula, the neglect of a back-reaction approximation, and the highly efficient density functional tight-binding method. We study the hot electron dynamics in a series of H- and F-terminated silicon nanocrystals (NCs) containing up to several hundred atoms. We explain the slower electron cooling dynamics in F-terminated NCs by the larger energy gaps between the adjacent electronic states in these systems as well as their slower fluctuations. We conclude that both the mass and chemical identity of the surface termination groups equally influence the electron dynamics, on average. However, the mass effect becomes dominant for higher-energy excitations. We find that the electron decay dynamics in F-terminated NCs has a greater sensitivity to the mass of the surface ligands than do the H-terminated NCs and explain this observation by the details of the electron-phonon coupling in the systems. We find that in the H-terminated NCs, electronic transitions in the cooling process occur predominantly between the surface states, whereas in F-terminated Si NCs, both surface and NC core states are coupled to the nuclear vibrations. We find that electron energy relaxation is accelerated in larger NCs and attribute this effect to the higher densities of states and smaller energy gaps in these systems.
我们开发了一种新的快速方法，用于对原子系统中电子态密集流形中发生的激发态动力学进行建模。该方法利用了修正的朗道 - 齐纳公式、忽略反向反应近似以及高效的密度泛函紧束缚方法。我们研究了一系列含有多达数百个原子的H端和F端硅纳米晶体（NCs）中的热电子动力学。我们解释了F端NCs中电子冷却动力学较慢的原因，是这些系统中相邻电子态之间的能隙较大以及它们的波动较慢。我们得出结论，平均而言，表面终止基团的质量和化学特性对电子动力学的影响相同。然而，对于高能激发，质量效应占主导。我们发现F端NCs中的电子衰减动力学对表面配体质量的敏感性比H端NCs更高，并通过系统中电子 - 声子耦合的细节解释了这一观察结果。我们发现，在H端NCs中，冷却过程中的电子跃迁主要发生在表面态之间，而在F端硅NCs中，表面态和NC核心态都与核振动耦合。我们发现，在较大的NCs中电子能量弛豫加速，并将这种效应归因于这些系统中更高的态密度和更小的能隙。
