Multidoping of Si Cages: High Spin States beyond the Single-Dopant Septet Limit

Density-functional theory based global geometry optimization is employed to systematically scrutinize the possibility of multidoping of hydrogenated Si clusters to achieve high spin states beyond the septet limit of a single-atom dopant. While our unbiased configurational search reveals that the previously suggested Si₁₈H₁₂ double hexagonal prism structure is generally too small to accommodate two dopants in magnetized state, the larger Si₂₄H₂₄ cage turns out to be suitable for such applications. For dimer dopants M₂⁺ = Cr₂⁺, Mn₂⁺, and CrMn⁺, the structural integrity of the host cage is conserved in the ground-state structure of corresponding M₂⁺@Si₂₄H₂₄ aggregates, as is the unusually high spin state of the guest dopant, which in the case of Cr₂⁺ already exceeds the single-atom dopant septet limit by almost a factor of 2. Moreover, the possibility of further increasing the cluster spin moment by encapsulating an even larger number of dopants into a suitably sized hydrogenated Si cage is illustrated for the example of a (CrMn⁺)₂@Si₂₈H₂₈ aggregate with a total number of 18 unpaired electrons. These results strongly suggest multidoping of Si clusters as a viable route to novel cluster-based materials for magneto-optic applications.