Structure and stability of AlnMgm (n = 4–8, m = 1–3) clusters: Genetic algorithm and density functional theory approach

Abstract

Abstract The low-energy structures of AlnMgm (n = 4–8, m = 1–3) are determined by using the genetic algorithm coupled with a modified embedded-atom interatomic potential. The close-packed structures are preferable in energy for Al-Mg clusters and in most cases there exist a few isomers with close energies. The stabilities of the Al-Mg clusters are governed by Mg/Al ratios and the electronic configurations. The clusters with lower Mg/Al ratios are more stable. The valence molecular orbitals and the density of states consistently demonstrate that the electronic structures of Al-Mg clusters can be described by the jellium model but the 2S level interweaves with the 1D levels. Al6Mg corresponds to a magic number structure with pronounced stability and large energy gap; the 20 valence electrons form closed 1S21P61D102S2 shells. Natural bond orbital analysis indicates that magnesium transfer electrons to aluminum; the average charge on Mg atoms is 0.61, but the charge on Al atoms depends strongly on the number of the connected Mg atoms.