Abstract: The geometries of various isomers of heterofullerenes C_20-2nX_2n (X=B, N; n=1, 2, 3, 4) were fully optimized at the B3LYP/6-31G* density functional level of theory, and the corresponding frequency calculations at the same level were used to characterize the ground state structures. The substitutional patterns, electronic structure, strain, and aromaticity of these heterofullerenes have been investigated. In general, nitrogen doping could not significantly decrease the strain of the cage. The strain of C₁₂N₈ was even larger than that of C₂₀, this nitrogen analogue was extraordinarily unstable. The two most stable isomers of C₁₈B2, 1,14-C₁₈B₂ and 1,3-C₁₈B₂, both have large HOMO-LUMO gaps and binding energies. They were highly aromatic. The strains of these two molecules were very small, compared with that of C₂₀.1,14-C₁₈B₂ and 1,3-C₁₈B₂ were predicted to be highly stable small heterofullerenes, these two configurational isomers could be distinguished fromeach other by their IR spectra.

Key words: Fullerene C₂₀, Boron- or nitrogen-doped, Structure, Stability, Density functional theory