Calculated Magnetic and Geometric Structures of Neutral Copper Oxide Clusters

The ground state geometric structures and electron configurations of subnanometer neutral copper oxide clusters are calculated with density functional theory. By comparing the results across almost 40 clusters, ranging between Cu₃O₃ and Cu₁₆O₈, we find evidence for strong ferromagnetic coupling that is responsible for increasing the number of unpaired electrons as Cu atoms are incremented away from the (Cu₂O)_n stoichiometry. The closed-shell (Cu₂O)_n clusters are nonmagnetic, whereas all other clusters exhibit varying degrees of magnetic susceptibility. The majority of the clusters considered in this manuscript have not been previously evaluated. Natural bonding orbital and Bader charge analysis reveal a nearly linear correlation between the charge transfer between Cu and O atoms and their local spin magnetic moments. Further, a relationship between the coordination of O atoms composing the cluster and their local magnetic moment is found. Bridging O atoms (μ2-O) typically exhibit large local magnetic moments, whereas the local magnetic moment is quenched by tetrahedrally coordinated (μ4-O) atoms. Thus, clusters containing Cu(II) atoms contain a large total magnetic moment, whereas Cu(I) atom clusters generally exhibit a small total magnetic moment and terminal Cu atom structures.