Many‐body effects on structures of small Ca 2+ Ar n clusters

The structure and stabilities of Ca 2+ Ar n ( 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 (Ca 2+ ‐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 Ca 2+ Ar n clusters, we use the so‐called basin‐hopping method of Wales et al. We show that in the equilibrium structures of Ca 2+ Ar n clusters, the Ca 2+ cation is always solvated by argon clusters. For n = 2, we have found a strong competition between the symmetric linear shape ( D ∞ ) 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 Ca 2+ Ar 3 is planar ( D 3h ), but a second three‐dimensional isomer with a pyramidal C 3v symmetry exists. The absolute minimum of Ca 2+ Ar 4 is a regular tetrahedron, and that of Ca 2+ Ar 6 , 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. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011