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arXiv 0904.4387cond-mat.mtrl-scicond-mat.other
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Mg(0001)表面原子氢吸附和初期氢化的密度泛函理论研究

Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: A density-functional theory study

Yanfang Li, Ping Zhang, Bo Sun, Yu Yang, Yinghui Wei

摘要:

采用密度泛函理论和超原胞方法研究了氢原子在Mg(0001)表面的吸附.覆盖度的吸附结构和能量的依赖性系统地研究了广泛的覆盖度和吸附位点。在覆盖范围$0<Θ<1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendecy to the formation of H islands (clusters) when increasing the coverage within the region $ 0<Θ<1.0中。原子氢的表面扩散路径能量学,以及氢从表面渗透到次表面的激活势垒,也提出了在低覆盖率。在高覆盖率下$1.00<Θ<2.0, it is found that the coadsorption configuration with 1.0 monolayer of H's residing on the surface fcc sites and the remaining monolayer of H's occupying the subsurface tetra-I sites is most energetically favourable. The resultant H-Mg-H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH$ _{2}$的态密度。H/Mg(0001)系统的其他性质,包括电荷分布、晶格弛豫、功函数和电子态密度,也进行了详细的研究和讨论。指出在表面氢化过程中H-Mg化学键表现出离子/共价的混合特征。

英文摘要:

We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage and adsorption sites. In the coverage range $0<Θ<1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendecy to the formation of H islands (clusters) when increasing the coverage within the region $0<Θ<1.0. The on-surface diffusion path energetics of atomic hydrogen, as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites, are also presented at low coverage. At high coverage of $1.00<Θ<2.0, it is found that the coadsorption configuration with 1.0 monolayer of H's residing on the surface fcc sites and the remaining monolayer of H's occupying the subsurface tetra-I sites is most energetically favourable. The resultant H-Mg-H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH$_{2}$ in the density of states. The other properties of the H/Mg(0001) system, including the charge distribution, the lattice relaxation, the work function, and the electronic density of states, are also studied and discussed in detail. It is pointed out that the H-Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.

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