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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Simulation of surface processes
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Simulation of surface processes

机译：模拟表面过程

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Computer simulations of surface processes can reveal unexpected insight regarding atomic-scale structure and transitions. Here, the strengths and weaknesses of some commonly used approaches are reviewed as well as promising avenues for improvements. The electronic degrees of freedom are usually described by gradient-dependent functional within Kohn-Sham density functional theory. Although this level of theory has been remarkably successful in numerous studies, several important problems require a more accurate theoretical description. It is important to develop new tools to make it possible to study, for example, localized defect states and band gaps in large and complex systems. Preliminary results presented here show that orbital density-dependent func-tionals provide a promising avenue, but they require the development of new numerical methods and substantial changes to codes designed for Kohn-Sham density functional theory. The nuclear degrees of freedom can, in most cases, be described by the classical equations of motion;however, they still pose a significant challenge, because the time scale of interesting transitions, which typically involve substantial free energy barriers, is much longer than the time scale of vibrations-often 10 orders of magnitude. Therefore, simulation of diffusion, structural annealing, and chemical reactions cannot be achieved with direct simulation of the classical dynamics. Alternative approaches are needed. One such approach is transition state theory as implemented in the adaptive kinetic Monte Carlo algorithm, which, thus far, has relied on the harmonic approximation but could be extended and made applicable to systems with rougher energy landscape and transitions through quantum mechanical tunneling.
机译：表面过程的计算机模拟可以揭示有关原子尺度结构和转变的意想不到的见识。在此，对一些常用方法的优缺点进行了回顾，并提出了有希望的改进途径。电子自由度通常由Kohn-Sham密度泛函理论中的梯度依赖泛函描述。尽管这种理论水平已经在众多研究中取得了显著成功，但一些重要问题仍需要更准确的理论描述。重要的是要开发新的工具，以便研究例如大型和复杂系统中的局部缺陷状态和带隙。此处给出的初步结果表明，依赖于轨道密度的函数提供了一种有希望的途径，但是它们需要开发新的数值方法以及对为Kohn-Sham密度泛函理论设计的代码进行重大更改。在大多数情况下，核自由度可以用经典的运动方程式描述；但是，它们仍然构成了巨大的挑战，因为有趣的跃迁的时间尺度通常比自由能垒要长得多，通常涉及大量的自由能垒。振动的时间尺度-通常为10个数量级。因此，经典动力学的直接模拟无法实现扩散，结构退火和化学反应的模拟。需要替代方法。一种这样的方法是在自适应动力学蒙特卡洛算法中实现的过渡态理论，到目前为止，它已依赖于谐波近似，但可以扩展并适用于具有较粗糙能量分布和通过量子机械隧穿进行过渡的系统。

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