Evolution of the atomic and electronic structures of CuO clusters: a comprehensive study using the DFT approach

One of the most fundamental aspects of cluster science is to understand the structural evolution at the atomic scale. In this connection, here we report a comprehensive study of the atomic and electronic structures of (CuO) clusters for n = 1 to 12 using DFT-based formalisms. Both the plane wave-based pseudo-potential approach and LCAO-MO-based method have been employed to obtain the ground state geometries of neutral, cation and anion copper oxide clusters. The results reveal that neutral copper oxide clusters favor a planar ring structure up to heptamer and from octamer onwards they adopt a three-dimensional motif with (CuO)₉ and (CuO)₁₂ forming a barrel-shaped layered structure. Detailed electronic structure analysis reveals that the transition of the atomic structure from 2D to 3D is guided by the energy balance of the Cu-O (d-p) and Cu-Cu (d-d) bonds. The removal of one electron from the cluster (cation) results in slightly stretched bonds while the addition of one electron (anion) showed compression in the overall geometries. The thermodynamic and electronic stability of these clusters has been analyzed by estimating their binding energy, ionization energy and electron affinity as a function of size. Remarkably, among these clusters, the octamer (CuO)₈ and dodecamer (CuO)₁₂ show higher binding energy and electron affinity (∼6.5 eV) with lower ionization energy (5.5-6.0 eV). This unique feature of the octamer and dodecamer indicates that they are very promising candidates for both oxidizing and reducing agents in different important chemical reactions.