氢在金属上扩散的深隧穿和经典跳跃
Simultaneous Deep Tunneling and Classical Hopping for Hydrogen Diffusion on Metals
摘要：
氢在金属上的扩散表现出丰富的量子行为，这是尚未完全理解。利用模拟，我们表明，许多氢扩散障碍可以分为那些与“抛物线顶”和那些与“宽顶”。随着温度的降低，在抛物顶势垒下，氢的扩散逐渐从经典的跳跃到浅隧穿再到深隧穿，并且在中等温度下仍存在明显的量子效应。与此相反，宽顶势垒的量子效应仅在低温下才变得重要，并且经典到量子的跃迁是尖锐的，在该跃迁处经典跳跃和深隧穿都发生。这种共存表明，不止一种机制有助于量子反应速率。传统的经典到量子交叉温度的定义对宽顶是无效的，我们给出了一个新的定义。扩展这一点，我们提出了一个模型来预测宽顶扩散的转变温度，理论和实验提供了一个通用的指导。
英文摘要：
Hydrogen diffusion on metals exhibits rich quantum behavior, which is not yet fully understood. Using simulations, we show that many hydrogen diffusion barriers can be categorized into those with "parabolic-tops" and those with "broad-tops". With parabolic-top barriers, hydrogen diffusion evolves gradually from classical hopping to shallow tunneling to deep tunneling as the temperature decreases, and noticeable quantum effects persist at moderate temperatures. In contrast, with broad-top barriers quantum effects become important only at low temperatures and the classical to quantum transition is sharp, at which classical hopping and deep tunneling both occur. This coexistence indicates that more than one mechanism contributes to the quantum reaction rate. The conventional definition of the classical to quantum crossover temperature is invalid for the broad-tops, and we give a new definition. Extending this we propose a model to predict the transition temperature for broad-top diffusion, providing a general guide for theory and experiment.
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