Wijzenbroek M, Kroes G J
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA, Leiden, The Netherlands.
Phys Chem Chem Phys. 2016 Aug 3;18(31):21190-201. doi: 10.1039/c6cp00291a.
In dynamics calculations of H2 dissociating on metal surfaces often clean, high-symmetry surfaces are used. Few such dynamics studies have been performed on surfaces with pre-adsorbed molecules, especially when also the motion of the surface and the adsorbate are considered. In this study, the dissociation of H2 on a carbon monoxide-covered Ru(0001) surface is considered. Ab initio molecular dynamics (AIMD) calculations are performed on this system using the PBE-vdW-DF2 functional, which accurately describes the reaction probability for H2 on Ru(0001). Using this functional, the reaction probability of H2 on the CO-covered Ru(0001) surface is found to be too low when compared to experiments. This suggests that exchange-correlation functionals that can describe the reaction of H2 on a bare metal surface are not in general able to describe the reaction of H2 on a CO-precovered surface of the same metal, with the same accuracy. However, it cannot be ruled out that the discrepancy between theory and experiment is partly due to an inhomogeneous coverage of the surface by CO in the experiments. The incorporation of the motion of the surface has only a small effect on the reaction probability. It is found that when including surface motion for this system, the size of the simulation cell can be important. Upon collision, a considerable amount of energy is transferred to the surface, causing the adsorbed CO molecules to move apart, which opens the surface for reaction. In order to obtain converged reaction probabilities with respect to the size of the simulation cell, at least a 3 × 3 simulation cell is needed, because in the smaller cell the CO molecules cannot be pushed apart as only a single independent CO molecule is present, also leading to less energy exchange with the surface.
在氢气在金属表面解离的动力学计算中，通常使用清洁的、高对称性的表面。很少有针对预吸附分子的表面进行此类动力学研究，尤其是当同时考虑表面和吸附质的运动时。在本研究中，考虑了氢气在一氧化碳覆盖的Ru(0001)表面的解离。使用PBE-vdW-DF2泛函对该体系进行了从头算分子动力学（AIMD）计算，该泛函能准确描述氢气在Ru(0001)上的反应概率。使用该泛函时，发现氢气在CO覆盖的Ru(0001)表面的反应概率与实验相比过低。这表明，能够描述氢气在裸金属表面反应的交换关联泛函，通常不能以相同的精度描述氢气在同一金属的CO预覆盖表面上的反应。然而，不能排除理论与实验之间的差异部分是由于实验中表面CO覆盖不均匀所致。纳入表面运动对反应概率的影响很小。研究发现，对于该体系，当考虑表面运动时，模拟单元的大小可能很重要。碰撞时，相当数量的能量转移到表面，导致吸附的CO分子分开，从而为反应打开表面。为了获得关于模拟单元大小收敛的反应概率，至少需要一个3×3的模拟单元，因为在较小的单元中，由于只有单个独立的CO分子，CO分子无法被推开，这也导致与表面的能量交换较少。
