The role of TM’s (M’s) d valence electrons in TM@X12 and M@X12 clusters

Using the density functional theory method, the icosahedral TM@X12 (M@X12) clusters (TM=Mn, Tc, Re; M=Zn, Cd, Hg; and X=Sn, Ge), which are composed of Sn12 (Ge12) shell covering a single TM (M) atom, have been systematically examined to explore the role of TM’s (M’s) d valence electrons playing in the clusters. The results show that the magnetism originate from the contribution of TM’s d valence electrons to TM@X12 clusters, where TM’s (M’s) d valence electrons are not included in the superatomic electronic states to TM@X12 (M@X12) clusters. Taking into account the structural stability (imaginary frequency, binding energy, embedding energy, and core-shell interaction) as well as the chemical stability (HOMO-LUMO gap) after, we proposed that TM@X12 and M@X12 clusters can be assigned as the protyle superatoms. Furthermore, the results suggest that M@C60 clusters can not be superatoms, because their negative embedding energies and the distance from the center atom (M) to C atom is larger than the sum of their Van Waals radii. Interestingly enough, we may obtain a simple judging method: for a magnetic superatom, the smaller the energy gap between the highest occupied magnetic state (HOMS) and Fermi level or HOMO (MOgap, or MFgap), the easier on the change of its spin magnetic moment.