Geometry, electronic structure, and energetics of copper-doped aluminum clusters

Using density functional theory and generalized gradient approximation for exchange-correlation potential, we have calculated the equilibrium geometri es and energetics of neutral and negatively charged AlnCu (n=11,12,13,14) c lusters. Unlike the alkali atom-doped aluminum clusters in the same size ra nge, the copper atom resides inside the aluminum cluster cage. Furthermore, the 3d and 4s energy levels of Cu hybridize with the valence electrons of Al causing a redistribution of the molecular orbital energy levels of the A l-n clusters. However, this redistribution does not affect the magic number s of AlnCu clusters that could be derived by assuming that Cu donates one e lectron to the valence levels of Al-n clusters. This behavior, brought abou t by the smaller size and large ionization potential of the copper atom, co ntributes to the anomalous properties of AlnCu- anions: Unlike AlnX- (X=alk ali atom), the mass ion intensities of AlnCu- are similar to those of Al-n( -). The calculated adiabatic electron affinities are also in very good agre ement with experiment. (C) 2001 American Institute of Physics.