Monovacancy and substitutional defects in hexagonal silicon nanotubes

We present a first-principles study of the geometrical and electronic structures of a hexagonal single-walled silicon nanotube with a monovacancy or a substitutional defect. The B, C, N, Al and P atoms are chosen as substitutional impurities. It is found that the defect such as a monovacancy or a substitutional impurity results in deformation of the hexagonal single-walled silicon nanotube. In both cases, a relatively localized unoccupied state near the Fermi level occurs due to this local deformation. The differences in geometrical and electronic properties of different substitutional impurities are discussed.