Probing the Geometric and Electronic Effects of Aluminum–Magnesium Clusters on Reactivity Toward Oxygen

Abstract

In this work, we perform detailed density functional theory (DFT) calculations to systematically study the composition-dependent structural, thermodynamic and electronic properties of Mg–Al alloy clusters with 55 atoms. It is found that the Al-rich clusters, such as Mg12Al43 and Mg12Al43− generally possess higher thermodynamic stability and exhibit distinctive electronic properties. Especially for Mg12Al43−, there is relatively large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), suggesting that the Mg12Al43− may possess higher resistance to the reactivity with oxygen. In addition, we also study single O atom and 3O2 adsorption on the Al55, Mg55, Mg12Al43 and Mg12Al43− clusters. Through comparing their adsorption energies, we find that the H1 sites (on the hollow site of one triangular facet among two edge and one vertex atoms) energetically are the most stable O adsorption site for all clusters. Most importantly, for 3O2 adsorbed on Mg12Al43 and Mg12Al43− clusters, replacing the Al atoms of Al55 cluster with Mg atoms can effectively weaken the adsorption of oxygen and enhance the resistance to oxidation.