Structure and magnetic properties of Cd9−nSe9Mnn and Cd9−nSe9Fen clusters (n = 0–9)

Abstract

Electronic, geometric, and magnetic structures of doped semiconductor clusters Cd9−nSe9Mnn and Cd9−nSe9Fen (n=0–9) are studied using density functional theory with the generalized gradient approximation. Polarizability, band gap widths, and density of states are obtained for the lowest total energy states in both series. The polarizability behavior is quite unexpected since the successive Mn and Fe substitutions lead to decreasing polarizability of the substituted clusters despite the metal atoms possessing substantially higher polarizabilities than the substituted Cd atoms. The band gap behavior is different for the two substitution types; namely, Fe substitutions resulted in a drastic decrease in the band gap width after the first substitution whereas the Mn substitutions produced a nearly monotonic decrease in the band gap width as the number of substituting atoms increased. It is found that the band gap of Cd9−nSe9Fen becomes smaller than that of the free-standing Fe9 cluster even at moderate amounts of Fe substitutions. It was also shown that in both series the metal atoms segregate as the number of substitutions increases and produce metallic clusters with Se atoms acting as ligands.