Institute of Materials Research, Materials Mechanics , Helmholtz-Zentrum Geesthacht , D-21502 Geesthacht , Germany.
Langmuir. 2018 Apr 24;34(16):4920-4928. doi: 10.1021/acs.langmuir.7b04261. Epub 2018 Apr 11.
We study the response of the surface stress to excess charge via ab initio simulation of metal surfaces in an external electric field. We focus on "simple" sp-bonded metals to gain insight into the mechanisms underlying electrocapillary coupling. Both the direct effect on the surface stress via charging of the bonds and the indirect effect resulting from the charge-induced relaxation are analyzed and discussed in relation to the trends of the coupling coefficients, which-owing to a Maxwell relation-are determined in terms of the response of the work function to strain. Al(111), Mg(0001), and Na(110) are investigated as prototypical sp-bonded metal surfaces with positive, vanishing, and negative coupling parameters, respectively. Mg(0001) and Al(111) exhibit an inward relaxation of the first atomic layer upon negative charging, whereas an outward relaxation occurs for Na(110). The indirect contribution of the relaxation to the coupling coefficient has the same sign as the total response and makes up about 30% of its magnitude for Al(111) and Na(110). Our study highlights that even the response behavior of the so-called simple metals is by no means readily captured within simple models.
我们通过对金属表面在外电场中的从头算模拟来研究表面应力对过剩电荷的响应。我们专注于“简单”的 sp 键合金属，以深入了解电毛细耦合的机制。我们分析和讨论了通过键合充电对表面应力的直接影响以及电荷诱导松弛产生的间接影响，这与耦合系数的趋势有关，由于麦克斯韦关系，耦合系数是根据功函数对应变的响应来确定的。Al(111)、Mg(0001)和 Na(110)被研究为具有正、零和负耦合参数的典型 sp 键合金属表面。对于负充电，Mg(0001)和 Al(111)的第一层原子向内松弛，而 Na(110)则向外松弛。松弛对耦合系数的间接贡献与总响应具有相同的符号，并且对于 Al(111)和 Na(110)来说，它占其大小的约 30%。我们的研究强调，即使是所谓的简单金属的响应行为也绝不是简单模型可以轻易捕捉到的。
