Structural evolution, stability, electronic and bonding properties of sodium-doped magnesium cluster cations

Abstract

Bimetallic sodium-doped magnesium cluster cations, NaMg n + (n= 2–12), have been investigated through a synergetic combination of the CALYPSO code and DFT calculations. The results reveal that the lowest-energy structures of NaMg n + exhibit linear, planar, triangular pyramid, pentagonal pyramid, and triangular prism topologies. The structures can be described as a substituted geometry of pure Mg clusters at the small size. Starting from n = 9, the dominant structures transform into a triangular prism-based configuration. Like anionic and neutral NaMg n clusters, the Na atom prefers the peripheral regions of the Mg n framework. Stability studies indicate NaMg4 + and NaMg10 + to be the~most stable clusters, which may benefit from their closed-shell electron structures. Analysis of the bonding nature shows stronger Mg-Mg interaction than the Na-Mg interaction in the NaMg4 + and NaMg10 + clusters. The reason is that covalent bonds are formed in the Mg-Mg regions, while there is no aggregation of electron density in the Na-Mg regions.