We perform the calculations on geometric and electronic structures of Si-doped heterofullerene C50Si10 and its derivatives,a 640Si20-CaoSi20 dimer and a C40Si20-based nanowire by using density-functional theory.The optimized configuration of the C40Si20-based nanowire exhibits a regular dumbbell-shaped chain nanostructure.The electronic structure calculations indicate that the HOMO-LUMO gaps of the heterofullerene-based materials can be greatly modified by substitutionally doping with Si atoms and show a decreasing trend with increase cluster size.Unlike the band structures of the conventional wide band gap silicon carbide nanomaterials,the C40Si20-based nanowire has a very narrow direct band gap of 0.087eV.