Fullerene C46: An unexpected non-classical cage

A systematic survey is performed on all isomers of fullerene C46 composed of squares, pentagons, hexagons. Density functional calculations demonstrate that the classical isomers generally follow the pentagon adjacency penalty rule. Unexpectedly, a non-classical isomer incorporating a square, i.e., C46-10-1 is predicted to be more energetically favorable than its lowest-energy classical rival. It is interesting that the non-classical structures with one or two squares exhibit unusually large HOMO–LUMO gaps. The relative thermodynamical stability is evaluated for several low-lying isomers in terms of the Gibbs function. The maximum pyramidization angles are also introduced to evaluate their stability.