Nattino Francesco, Costanzo Francesca, Kroes Geert-Jan
Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
J Chem Phys. 2015 Mar 14;142(10):104702. doi: 10.1063/1.4913979.
Accurately modeling the chemisorption dynamics of N2 on metal surfaces is of both practical and fundamental interest. The factors that may have hampered this achievement so far are the lack of an accurate density functional and the use of approximate methods to deal with surface phonons and non-adiabatic effects. In the current work, the dissociation of molecular nitrogen on W(110) has been studied using ab initio molecular dynamics (AIMD) calculations, simulating both surface temperature effects, such as lattice distortion, and surface motion effects, like recoil. The forces were calculated using density functional theory, and two density functionals were tested, namely, the Perdew-Burke-Ernzerhof (PBE) and the revised PBE (RPBE) functionals. The computed dissociation probability considerably differs from earlier static surface results, with AIMD predicting a much larger contribution of the indirect reaction channel, in which molecules dissociate after being temporally trapped in the proximity of the surface. Calculations suggest that the surface motion effects play a role here, since the energy transfer to the lattice does not allow molecules that have been trapped into potential wells close to the surface to find their way back to the gas phase. In comparison to experimental data, AIMD results overestimate the dissociation probability at the lowest energies investigated, where trapping dominates, suggesting a failure of both tested exchange-correlation functionals in describing the potential energy surface in the area sampled by trapped molecules.
准确模拟氮气在金属表面的化学吸附动力学具有实际和基础研究的双重意义。迄今为止，可能阻碍这一目标实现的因素包括缺乏精确的密度泛函以及使用近似方法处理表面声子和非绝热效应。在当前工作中，利用从头算分子动力学（AIMD）计算研究了分子氮在W(110)上的解离，模拟了诸如晶格畸变等表面温度效应以及诸如反冲等表面运动效应。使用密度泛函理论计算力，并测试了两种密度泛函，即Perdew-Burke-Ernzerhof（PBE）和修正的PBE（RPBE）泛函。计算得到的解离概率与早期的静态表面结果有很大不同，AIMD预测间接反应通道的贡献要大得多，在间接反应通道中，分子在暂时被困在表面附近后解离。计算表明，表面运动效应在此起作用，因为向晶格的能量转移不允许被困在靠近表面的势阱中的分子回到气相。与实验数据相比，AIMD结果高估了在所研究的最低能量下的解离概率，在这些能量下捕获起主导作用，这表明两种测试的交换关联泛函在描述被困分子采样区域的势能面时均失效。
