Glowacki David R, Rodgers W J, Shannon Robin, Robertson Struan H, Harvey Jeremy N
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
Department of Computer Science, University of Bristol, Bristol BS8 1UB, UK.
Philos Trans A Math Phys Eng Sci. 2017 Apr 28;375(2092). doi: 10.1098/rsta.2016.0206.
The extent to which vibrational energy transfer dynamics can impact reaction outcomes beyond the gas phase remains an active research question. Molecular dynamics (MD) simulations are the method of choice for investigating such questions; however, they can be extremely expensive, and therefore it is worth developing cheaper models that are capable of furnishing reasonable results. This paper has two primary aims. First, we investigate the competition between energy relaxation and reaction at 'hotspots' that form on the surface of diamond during the chemical vapour deposition process. To explore this, we developed an efficient reactive potential energy surface by fitting an empirical valence bond model to higher-level electronic structure theory. We then ran 160 000 NVE trajectories on a large slab of diamond, and the results are in reasonable agreement with experiment: they suggest that energy dissipation from surface hotspots is complete within a few hundred femtoseconds, but that a small fraction of CH does in fact undergo dissociation prior to the onset of thermal equilibrium. Second, we developed and tested a general procedure to formulate and solve the energy-grained master equation (EGME) for surface chemistry problems. The procedure we outline splits the diamond slab into system and bath components, and then evaluates microcanonical transition-state theory rate coefficients in the configuration space of the system atoms. Energy transfer from the system to the bath is estimated using linear response theory from a single long MD trajectory, and used to parametrize an energy transfer function which can be input into the EGME. Despite the number of approximations involved, the surface EGME results are in reasonable agreement with the NVE MD simulations, but considerably cheaper. The results are encouraging, because they offer a computationally tractable strategy for investigating non-equilibrium reaction dynamics at surfaces for a broader range of systems.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.
振动能量转移动力学在气相之外对反应结果产生影响的程度仍是一个活跃的研究问题。分子动力学（MD）模拟是研究此类问题的首选方法；然而，它们的计算成本可能极高，因此开发能够给出合理结果的更廉价模型是值得的。本文有两个主要目标。首先，我们研究在化学气相沉积过程中金刚石表面形成的“热点”处能量弛豫与反应之间的竞争。为了探究这一点，我们通过将经验价键模型拟合到更高层次的电子结构理论，开发了一个有效的反应势能面。然后我们在一大块金刚石平板上运行了160000条NVE轨迹，结果与实验结果合理相符：它们表明表面热点的能量耗散在几百飞秒内完成，但实际上一小部分CH在热平衡开始之前确实发生了离解。其次，我们开发并测试了一种通用程序，用于制定和求解表面化学问题的能量粒化主方程（EGME）。我们概述的程序将金刚石平板分为系统和浴组件，然后在系统原子的构型空间中评估微正则过渡态理论速率系数。利用来自单个长MD轨迹的线性响应理论估计从系统到浴的能量转移，并用于参数化一个能量转移函数，该函数可输入到EGME中。尽管涉及许多近似，但表面EGME结果与NVE MD模拟合理相符，但成本要低得多。这些结果令人鼓舞，因为它们为研究更广泛系统表面的非平衡反应动力学提供了一种计算上可行的策略。本文是主题为“气相、凝聚相和界面中非平衡和非统计动力学的理论与计算研究”特刊的一部分。
