High-valence cluster electron configuration

As a result of this electron-filling scheme for jellium clusters, the magic numbers for closed shell configurations in a jellium cluster are very different from those in free atoms. The first magic number of chemical significance in a jellium sphere is the 20 valence electron configuration of white phosphorus P4 and other isoelectronic species of the type E4 (E = As, Sb, Bi) and E4" (E = Si, Ge, Sn, Pb), which are shown by the NICS method to be highly aromatic systems [39, 79]. 

Consider the example of the Na4 cluster [16], In its high-symmetry configuration the four sodium atoms are arranged in a tetrahedron. The four 3s valence orbitals in this conformation form a and t2 symmetrised orbitals. In the Na4 system the valence electronic configuration is producing electronic terms... 

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