Han Yong, Evans James W
Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA and Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA.
J Chem Phys. 2015 Oct 28;143(16):164706. doi: 10.1063/1.4934349.
Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C6-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001).
进行了大规模的第一性原理密度泛函理论计算，以研究钌（Ru）吸附原子在Ru(0001)支撑的单层石墨烯（G）上的吸附和扩散。由于晶格失配，石墨烯片呈现出周期性的莫尔超结构。在一个莫尔晶胞内，有三个不同的区域：面心立方（fcc）、六方密堆积（hcp）和丘状区域，其中C6环中心分别位于fcc位点、hcp位点和Ru(0001)的表面Ru原子上方。在这些不同区域的特定位置评估Ru吸附原子的吸附能。我们发现在fcc区域中C原子上方的吸附位点结合最强，其次是hcp区域，然后是这两个区域之间的fcc-hcp边界（脊），而在丘状区域结合最弱。其行为与Habenicht等人[《顶级催化》57, 69 (2014)]从小晶胞计算中观察到的相似，这与之前的大规模计算不同。我们确定了fcc区域中心附近局部扩散的最小能量路径，并获得了约0.48 eV的局部扩散势垒。我们还估计在脊区域的局部扩散势垒要低得多。这些势垒以及吸附能变化的信息有助于开发一个关于Ru吸附原子全局势能面的现实模型。这反过来又能够进行模拟研究，阐明在Ru沉积到G/Ru(0001)上的过程中，Ru纳米团簇的扩散介导定向组装。
