Department of Chemistry, State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China.
J Chem Phys. 2010 Feb 14;132(6):064502. doi: 10.1063/1.3317475.
The quantum instanton approximation is extended to investigate dynamical processes of hydrogen on surface, from surface to subsurface, and between interior sites in nickel lattice. The path integral Monte Carlo and adaptive umbrella sampling techniques are employed to manipulate the quantum instanton formula. The free energy profiles along reaction paths, temperature dependence of free energies, and rates as well as diffusion coefficients are calculated for each process. The results manifest that the motions of nickel atoms beneath the surface have little effect on the hydrogen diffusion on Ni(111), and the hydrogen at the fcc binding site is much easier to get into bulk nickel than the one at the hcp site. The temperature dependence of free energy profiles also reveals that the hydrogen in the subsurface octahedral vacancy and interior tetrahedral vacancy becomes unstable at low temperatures, which proposes a temperature dependence of reaction mechanism. In addition, the relaxations of the lattices dramatically lower the free energy barriers except for the process of the hydrogen diffusion on Ni(111). The quantum motions of the lattice atoms affect the free energies little at 300 K, but they hinder the rates by 20%-40% compared with the classical motions of lattice atoms.
量子瞬子近似被扩展用于研究氢在表面、从表面到次表面以及镍晶格内部位置之间的动力学过程。路径积分蒙特卡罗和自适应伞状采样技术被用于操纵量子瞬子公式。对于每个过程，计算了沿反应路径的自由能曲线、自由能对温度的依赖性、速率以及扩散系数。结果表明，表面下镍原子的运动对 Ni(111)上的氢扩散几乎没有影响，并且 fcc 结合位上的氢比 hcp 位上的氢更容易进入体相镍。自由能曲线的温度依赖性还表明，次表面八面体空位和内部四面体位点中的氢在低温下变得不稳定，这提出了反应机制的温度依赖性。此外，除了 Ni(111)上的氢扩散过程外，晶格的弛豫极大地降低了自由能垒。在 300 K 时，晶格原子的量子运动对自由能的影响很小，但与晶格原子的经典运动相比，它们会使速率降低 20%-40%。
