Density function study transition metal chromium-doped alkali clusters: the finding of magnetic superatom
The structures, stabilities and magnetic properties of CrXn (X = Na, Rb and Cs; n up to 9) clusters are studied using density functional theory to search for the stable magnetic superatoms. The geometrical optimisations indicate the ground-state structures of CrXn evolve toward a close packed structure with an interior Cr atom surrounded by X atoms as the cluster size increase. Their stabilities are analysed by the relative energy, gain in energy (ΔE(n)) and the highest unoccupied molecular orbital and lowest unoccupied molecular orbital gaps. Furthermore, the magnetic moments of CrXn clusters show an odd–even oscillation. Here, we mainly focus on the CrX7 (X = Na, Rb and Cs) clusters due to the same valence count as the known stable magnetic superatoms VNa8, VCs8 and TiNa9. Although these clusters all have a filled electronic configuration 1S21P6 and large magnetic moment 5 μB, our studies indicate that only CrNa7 is highly stable compared to its nearest neighbours, while CrRb7 and CrCs7 clusters are less stable. This suggests that Cr-doped Na7 is most appropriate for filled electronic configuration and CrNa7 is shown to be a stable magnetic superatom. More interesting, we find CrRb8 and CrCs8 with the filled electronic configuration 1S21P6 have higher stability and large magnetic moment 6 μB in their respective series.
