Magnetic Properties of Cu_mO_n Clusters: A First Principles Study

Experimental evidence shows that small Cu₂O nanoparticles exhibit ferromagnetic or paramagnetic properties, allowing for the promising possibility to recycle the catalyst Cu₂O easily in wastewater treatment. In this paper, theoretical calculation studying the magnetic property of copper/oxide clusters is reported. A series of Cu_mO_n ((m, n) = (4, 1); (4, 2); (4, 5); (16, 15); (28, 15); (44, 15); (28, 27)) clusters were investigated using generalized gradient approximation (GGA) and the Hubbard U (GGA+U) method within density functional theory (DFT). It is found that the electronic structures of bulk Cu₂O calculated by the GGA and GGA+U are similar. The structures of Cu_mO_n ((m, n) = (4, 1); (4, 2); (4, 5)) are all planar. For the bulk-product Cu_mO_n ((m, n) = (16, 15); (28, 15); (44, 15); (28, 27)), O atoms prefer to be the outermost atoms. We classified two types of clusters on the basis of their O to Cu atomic ratios. One is O-rich clusters, i.e., Cu₄O₅, Cu₁₆O₁₅, and Cu₂₈O₂₇. The other is O-poor clusters, i.e., Cu₄O, Cu₄O₂, Cu₂₈O₁₅, and Cu₄₄O₁₅. The calculation results show that the O-rich clusters have longer average Cu−Cu bonds and larger binding energy than those of the O-poor ones. More interestingly, the former are magnetic and give ferromagnetic ordering while the latter are nonmagnetic. The hydrogenation of O-terminated clusters can improve its stability but suppress its magnetism. The study may be extremely useful for the potential applications of Cu₂O nanopaticles in the catalysis and semiconductor fields.