First principles study on the structural evolution and properties of (MCl)n (n = 1–12, M = Cu, Ag) clusters

Abstract

The structural evolution of (MCl)_n (M = Cu, Ag, n = 1–12) clusters has been explored using a first principles global minimization technique, namely, a genetic algorithm from density functional theory geometry optimization (GA-DFT). Benchmark calculations indicate that the method used in this work is reliable in predicting the energetic sequences of different isomers of (CuCl)₆ clusters compared to the high-level coupled cluster method. The computational results indicate that the structures of (CuCl)_n and (AgCl)_n clusters share many similarities. The global minima of (MCl)_n clusters are planar and nonplanar monocyclic structures up to n = 5, and multi-ring or catenane structures when n ≥ 6. The characters of the intramolecular interactions of (AgCl)₃, (CuCl)₃, (CuCl)₄ and (CuCl)₆ clusters have been studied by the noncovalent interactions (NCI) index. The electronic and bonding properties of (CuCl)₃ and (AgCl)₃ clusters are analyzed. At a higher level, the refined energies of the isomers, the binding energies and the second difference of binding energies are calculated, and are examined as a function of the cluster size. Several promising sizes of higher stability and symmetry have been discovered. In particular, we find that the cluster adopts a new folding manner, tube conformation, at n = 6, 9 and 12, where they are more stable than the adjacent clusters; moreover, they are aromatic.