Structures and stabilities of B7, B7+ and B7− clusters

Ab initio (MP2) and density functional theory (DFT) calculations for six neutral (structures 1–6), six cationic (structures 1+–6+) and six anionic (structures 1−–6−) isomers of B7 clusters have been performed. With only a few exceptions, all isomers are genuine minima. The hexagon capped by an atom structures (C2v symmetry) are global minima for B7 (1) and B7− (1−) and the hexagonal pyramid structure (C6v symmetry) is the most stable B7+ (1+). The aromatic natures of 1 and 1+, as well as the anti-aromatic character of 1− are also discussed.