de Lara-Castells María Pilar, Fernández-Perea Ricardo, Madzharova Fani, Voloshina Elena
Instituto de Física Fundamental (CSIC), Serrano 123, E-28006 Madrid, Spain.
Instituto de Estructura de la Materia (CSIC), Serrano 123, E-28006 Madrid, Spain.
J Chem Phys. 2016 Jun 28;144(24):244707. doi: 10.1063/1.4954772.
The adsorption of noble gases on metallic surfaces represents a paradigmatic case of van-der-Waals (vdW) interaction due to the role of screening effects on the corrugation of the interaction potential [J. L. F. Da Silva et al., Phys. Rev. Lett. 90, 066104 (2003)]. The extremely small adsorption energy of He atoms on the Mg(0001) surface (below 3 meV) and the delocalized nature and mobility of the surface electrons make the He/Mg(0001) system particularly challenging, even for state-of-the-art vdW-corrected density functional-based (vdW-DFT) approaches [M. P. de Lara-Castells et al., J. Chem. Phys. 143, 194701 (2015)]. In this work, we meet this challenge by applying two different procedures. First, the dispersion-corrected second-order Möller-Plesset perturbation theory (MP2C) approach is adopted, using bare metal clusters of increasing size. Second, the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)] is applied at coupled cluster singles and doubles and perturbative triples level, using embedded cluster models of the metal surface. Both approaches provide clear evidences of the anti-corrugation of the interaction potential: the He atom prefers on-top sites, instead of the expected hollow sites. This is interpreted as a signature of the screening of the He atom by the metal for the on-top configuration. The strong screening in the metal is clearly reflected in the relative contribution of successively deeper surface layers to the main dispersion contribution. Aimed to assist future dynamical simulations, a pairwise potential model for the He/surface interaction as a sum of effective He-Mg pair potentials is also presented, as an improvement of the approximation using isolated He-Mg pairs.
由于屏蔽效应在相互作用势的起伏中所起的作用，稀有气体在金属表面的吸附代表了范德华（vdW）相互作用的一个典型案例[J. L. F. Da Silva等人，《物理评论快报》90, 066104 (2003)]。氦原子在Mg(0001)表面的吸附能极小（低于3毫电子伏特），以及表面电子的离域性质和迁移率，使得He/Mg(0001)体系极具挑战性，即便对于最先进的基于vdW校正密度泛函（vdW-DFT）的方法也是如此[M. P. de Lara-Castells等人，《化学物理杂志》143, 194701 (2015)]。在这项工作中，我们通过应用两种不同的程序来应对这一挑战。首先，采用色散校正的二阶莫勒-普列斯特定理微扰理论（MP2C）方法，使用尺寸不断增大的裸金属簇。其次，在耦合簇单双激发和微扰三激发水平上应用增量法[H. Stoll，《化学物理杂志》97, 8449 (1992)]，使用金属表面的嵌入簇模型。两种方法都提供了相互作用势反起伏的明确证据：氦原子更喜欢顶位，而不是预期的空位。这被解释为金属对顶位构型中氦原子进行屏蔽的一个特征。金属中的强屏蔽明显反映在相继更深的表面层对主要色散贡献的相对贡献上。为了辅助未来的动力学模拟，还提出了一个用于He/表面相互作用的成对势模型，它是有效He-Mg对势的总和，作为对使用孤立He-Mg对近似的一种改进。
