Structure, stability and bonding features of AlnSim clusters

Abstract

Al–Si alloys have excellent properties for building engine blocks, and their microstructures have important effect on the performance. Investigations on the electronic structures of Al–Si clusters help to understand the microstructural evolution and improve the properties of the alloys. This paper studies the geometric structures, stabilities and bonding features of AlnSim (n,m = 2,4,6 and n + m = 8,10,12) clusters by using genetic algorithm combined with density functional theory and QCISD models. The results show there are a lot of isomers with close energies, and the geometric structures suggest no obvious Al–Si segregation. The electronic structures of the Al–Si clusters are similar to the metal clusters; the density of states of the aluminum-rich clusters agrees with the jellium shells. Doping silicon enhances the stabilities of the aluminum clusters significantly; the binding energies increase considerably with the Si/Al ratios. The bonding features and energetics demonstrate the Si–Si and Si–Al interactions are much stronger than the Al–Al interaction. As the dispersion of Si atoms will form more Si–Al bonds, it suggests the silicon atoms can form highly dispersed states in the hypoeutectic and eutectic alloys (≤ 12.6% Si).