Reaction and relaxation at surface hotspots: using molecular dynamics and the energy-grained master equation to describe diamond etching.
Reaction and relaxation at surface hotspots: using molecular dynamics and the energy-grained master equation to describe diamond etching.
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DOI：
10.1098/rsta.2016.0206
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发表时间：
2017-04-28
期刊：
影响因子：
--
通讯作者：
Harvey JN
中科院分区：
文献类型：
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作者：
Glowacki DR;Rodgers WJ;Shannon R;Robertson SH;Harvey JN
振动能量传递动力学在多大程度上影响气相以外的反应结果仍然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，它们可能非常昂贵，因此值得开发能够提供合理结果的更便宜的模型。本文有两个主要目标。首先，我们研究了化学气相沉积过程中金刚石表面形成的“热点”处的能量弛豫和反应之间的竞争。为了探索这一点，我们通过将经验价键模型拟合到更高层次的从头算电子结构理论，开发了一种有效的反应势能表面。然后，我们在一大块金刚石上运行了 160 000 个 NVE 轨迹，结果与实验相当一致：它们表明表面热点的能量耗散在几百飞秒内完成，但一小部分 CH3 实际上在热平衡开始之前就发生了解离。其次，我们开发并测试了一个通用程序来制定和求解表面化学问题的能量粒度主方程（EGME）。我们概述的程序将金刚石板分成系统和熔池组件，然后评估系统原子构型空间中的微规范过渡态理论速率系数。使用线性响应理论从单个长 MD 轨迹估计从系统到浴的能量传递，并用于参数化可输入 EGME 的能量传递函数。尽管涉及大量近似值，表面 EGME 结果与 NVE MD 模拟相当一致，但成本要低得多。结果令人鼓舞，因为它们提供了一种计算上易于处理的策略，用于研究更广泛系统的表面非平衡反应动力学。本文是主题“气相、凝聚相和界面非平衡和非统计动力学的理论和计算研究”的一部分。
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 ab initio 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 CH3 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’.