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The equilibrium geometries, total energies, and vibrational frequencies of anions X2Y2 − (X = C, Si, Ge and Y = N, P, As) are theoretically investigated with density functional theory (DFT) method. Our calculation shows that for C2N2 − species, the D 2h isomer is the most stable four-membered structure, and for other species the C 2v isomer in which two X atoms are contrapuntal is the most stable structure at the B3LYP/6-311 +G* level. Wiberg bond index (WBI) and negative nucleus-independent chemical shift (NICS) value indicate the existence of delocalization in stable X2Y2 − structures. A detailed molecular orbital (MO) analysis further reveals that stable isomers of these species have strongly aromatic character, which strengthens the structural stability and makes them closely connected with the concept of aromaticity.

The equilibrium geometries, total energies and harmonic vibrational frequencies of planar low-lying states for Si 2 BX (X = Li, K, O, S) species are investigated at B3LYP/6-311+G ∗ and B3PW91/6-311+G ∗ levels. The research results show that for Si 2 BLi, Si 2 BK and Si 2 BS species, the C 2 v isomer is the most stable planar structure, and for Si 2 BO species, the C s isomer is the most stable planar structure. Negative nucleus independent chemical shift (NICS) values indicate the existence of aromaticity in planar structures for these species. A detailed molecular orbital (MO) analysis further reveals that a delocalized π MO for two isomers of Si 2 BX (X = Li, K, O, S) strengthens the structural stability and make these species show strongly aromatic character.

Clusters XSi 2 Y (X = Al, Ga and Y = P, As) are theoretically investigated using density functional theory (DFT) methods at the B3LYP/6-311+G* and B3PW91/6-311+G* levels of theory. The calculated results showed that for AlSi 2 P AlSi 2 As and PSi 2 Ga species, the C 2 v isomer is the ground state, respectively, whereas for GaSi 2 As species, the C s isomer is the ground state. The wiberg bond index (WBI) suggested the existence of delocalization. Negative nucleus-independent chemical shift (NICS) values indicated that a strong ring current exists in two isomers of those species. A detailed molecular orbital (MO) analysis further revealed that two isomers of these species have π aromaticity, and the two delocalized π electrons does agree well with the (4 n + 2) Huckel rule, which is closely connected with the concept of the aromaticity.