Departamento de Física Fundamental, Facultad de Ciencias, UNED, 28040 Madrid, Spain.
J Chem Phys. 2013 Dec 7;139(21):214305. doi: 10.1063/1.4834595.
Recently, it has been experimentally elucidated whether a V impurity in Al(n)V(+) clusters occupies an external or an internal site by studying their interaction with argon as a function of cluster size [S. M. Lang, P. Claes, S. Neukermans, and E. Janssens, J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. In the work presented here we studied, by means of density functional theoretic calculations, the structural and electronic properties of Al(n)V(+) clusters with n = 14-21 atoms, as well as the adsorption of a single Ar atom on them. For n < 17 the lowest energy structure of Al(n)V(+) is related to that of the pure Al(n+1)(+) cluster with the V atom substituting a surface Al atom. For n ≥ 17 the V impurity becomes embedded in the cluster, in agreement with the experimental results, and the clusters adopt a fcc-like structure instead of the icosahedral-like skeleton of pure Al(n+1)(+). We have studied the binding energy per atom, the second energy difference, and the V and Al atom separation energies, in comparison with those of pure Al(n+1)(+). We also studied the adsorption of atomic Ar on endohedral and exohedral V doped clusters. The optimized Ar adsorption geometries are formed with Ar on top of a surface atom (V for n < 17, and Al for n ≥ 17) without noticeable structural distortion of the host cluster. At the critical size (n = 17) of the exohedral-endohedral transition, the calculated Ar adsorption energy exhibits a drop and the Ar-cluster distance increases drastically, indicating that Ar becomes physisorbed rather than chemisorbed. All these results confirm the assumptions made by the experimentalists when interpreting their measurements.
最近，通过研究 Al(n)V(+) 团簇与氩气的相互作用作为团簇尺寸的函数，实验阐明了 V 杂质在 Al(n)V(+) 团簇中占据外部或内部位置[ S. M. Lang、P. Claes、S. Neukermans 和 E. Janssens，J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]。在本文中，我们通过密度泛函理论计算研究了具有 n = 14-21 个原子的 Al(n)V(+) 团簇的结构和电子性质，以及单个 Ar 原子在它们上的吸附。对于 n < 17，Al(n)V(+) 的最低能量结构与纯 Al(n+1)(+) 团簇的结构有关，其中 V 原子取代了表面 Al 原子。对于 n ≥ 17，V 杂质嵌入团簇中，与实验结果一致，团簇采用 fcc 类似结构而不是纯 Al(n+1)(+) 的二十面体骨架。我们研究了每个原子的结合能、第二能量差以及 V 和 Al 原子的分离能，并与纯 Al(n+1)(+) 的进行了比较。我们还研究了原子 Ar 在笼内和笼外掺杂 V 的团簇上的吸附。优化后的 Ar 吸附几何形状是在表面原子（对于 n < 17 为 V，对于 n ≥ 17 为 Al）上形成的，而没有明显的宿主团簇结构变形。在外层-内层转变的临界尺寸（n = 17）处，计算出的 Ar 吸附能下降，Ar-团簇距离急剧增加，表明 Ar 变成物理吸附而不是化学吸附。所有这些结果都证实了实验人员在解释他们的测量结果时所做的假设。
