Structure and Electronic Properties of Transition-Metal/Mg Bimetallic Clusters at Realistic Temperatures and Oxygen Partial Pressures

Composition, atomic structure, and electronic properties of TMxMgyOz clusters [transition metal (TM) = Cr, Ni, Fe, and Co, x + y <= 3] under realistic temperature T and oxygen partial pressure pO(2) conditions are explored using the ab initio atomistic thermodynamics approach. The low-energy isomers of the different clusters are identified using a massively parallel cascade genetic algorithm on the hybrid density-functional theory level. On analyzing a large set of data, we find that the fundamental gap E-g of the thermodynamically stable clusters is strongly affected by the presence of Mg-coordinated O-2 moieties. By contrast, the nature of the TM does not play a significant role in determining E-g. Using E-g of a cluster as a descriptor of its redox properties, our finding is against the conventional belief that the TM plays a key role in determining the electronic and therefore chemical properties of the clusters. High reactivity may be correlated more strongly with the oxygen content in the cluster than with any specific TM type.