Theoretical study on non-classical fullerene C54 with square(s) or heptagon(s)

To put insight into the structures and stability of non-classical fullerenes, density functional theory calculations were performed on both classical and non-classical isomers of fullerene C54. The calculated results demonstrate that the most stable isomer is classical and the classical isomers obey the pentagon adjacency penalty rule. For non-classical isomers with one or two squares, although they have fewer fused pentagons they are markedly disadvantageous in energy and unexpectedly, have larger HOMO-LUMO gaps compared with classical ones. The gap of one isomer with two squares is unusually up to 2.54 eV, closer to 2.76 eV of IPR-C60 at the same level of theory. For non-classical isomers with heptagon(s), the ones with a heptagon are more advantageous than the classical ones with the same number of B55 bonds, some of them are even more advantageous than some classical isomers with fewer B55 bonds. It is found that the pyramidization angles of vertexes involving in square are larger than other vertexes without involving in square and the pyramidization angles of vertexes shared by two pentagons and one heptagon is smaller than the pyramidization angles of vertexes shared by two pentagons and one hexagon. These findings suggest that the incorporation of square may lead to additional strain and unusual kinetic stability; and heptagon may release the strain in adjacent pentagon-pentagon bonds.