Structures and aromaticity of the planar XSi2Y (XÂ =Â Al, Ga and YÂ =Â P, As) clusters

Clusters XSi2Y (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 AlSi2P AlSi2As and PSi2Ga species, the C2v isomer is the ground state, respectively, whereas for GaSi2As species, the Cs 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 (4n + 2) Huckel rule, which is closely connected with the concept of the aromaticity.