Many-Body Effects on Structures of Small Ca2+Arn Clusters

The structure and stabilities of Ca2+Arn (n = 1-24) clusters are investigated using analytical potential functions. The energy of the systems, in its ground state, is described using additive potentials with V(Ca2+-Ar) and V(Ar-Ar) representing the pair potential interactions, and many-body effects are described using the interaction between dipoles induced by the calcium ion. To find the geometry of the lowest energy isomers of Ca2+Arn clusters, we use the so-called basin-hopping method of Wales et al. We show that in the equilibrium structures of Ca2+Arn clusters, the Ca2+ cation is always solvated by argon clusters. For n = 2, we have found a strong competition between the symmetric linear shape (D infinity) and the bent isomer (C-2v). The relative importance of the three-body interactions due to the presence of the induced dipoles on the Ar atoms can be inferred from the magnitude of the known Ar-2 interaction, and lead to a more stabilized linear structure. The global minimum of Ca2+Ar3 is planar (D-3h), but a second three-dimensional isomer with a pyramidal C-3v symmetry exists. The absolute minimum of Ca2+Ar4 is a regular tetrahedron, and that of Ca2+Ar6, is a regular octahedron. The particularly stable sizes with respect to their immediate neighbors were studied by calculating the second energy difference between size n and its immediate neighbors. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 652-660, 2011