Ames Laboratory, USDOE, Ames, Iowa 50011, USA.
J Chem Phys. 2013 Dec 14;139(22):224702. doi: 10.1063/1.4839595.
The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H2 molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H2 molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.
基于密度泛函理论的第一性原理计算系统研究了氢在双轴应变 Mg（0001）表面上的吸附、扩散和分子离解。当应变从压缩变为拉伸时，H 原子的吸附能呈线性增加，而其扩散势垒则呈相反的线性降低。H2 分子的离解势垒在拉伸应变区域呈线性降低。通过包括电荷密度差、投影态密度和 Mulliken 布居在内的化学键分析，阐明了应变对 H 原子吸附和 H2 分子离解的作用机制，提出了 s-p 电荷转移模型。随着晶格膨胀导致表面 Mg 原子轨道重叠减少，电荷从 p 态向 Mg 原子的 s 态转移，增强了 H s 和 Mg s 轨道的杂化。因此，H 与 Mg 表面的结合相互作用增强，从而降低了氢的原子扩散和分子离解势垒。我们的工作有助于理解和估计晶格变形对含镁储氢材料性能的影响。
