First-principle studies of the geometries and electronic properties of CumSin(2 ⩽m+n⩽ 7) clusters

Abstract

The equilibrium geometries and electronic properties of CumSin (2 ≤ m + n ≤ 7) clusters have been studied by using density functional theory at the B3LYP/6-311+G (d) level. Our results indicate that the structure of CuSin (n < 6) keeps the frame of the corresponding Sin cluster unchanged, while for CunSi clusters, the rectangular pyramid structure of Cu4Si is shown to be a building block in many structures of larger CunSi clusters. The growth patterns of CumSin clusters become more complicated as the number of Cu atoms increases. Both the binding energies and the fragmentation energies indicate that the Si-Si bond is stronger than the Cu-Si bond, and the latter is stronger than the Cu-Cu bond. Combining the fragmentation energies in the process CumSin → Cu+Cum-1Sin and the second-order difference Δ2E(m) against the number of Cu atoms of CumSin, we conclude that CumSin clusters with even number of Cu atoms have higher stabilities than those with odd m. According to frontier orbital analyses, there exists a mixed ionic and covalent bonding picture between Cu and Si atoms, and the Cu d orbitals contribute little to the Cu-Si bonding. For a certain cluster size (m + n = 3, 4, 5, 6, 7), the energy gaps of the most stable CumSin clusters show odd-even oscillation with changing m, the clusters with odd m exhibit stronger chemical reactivity than those with even m.