Theoretical exploration of the effects of germanium substitution on armchair single-walled carbon nanotubes

Armchair (5, 5) carbon nanotubes doped with germanium atoms (Ge, n = 1-4) were explored theoretically in this work. Density functional theory (DFT) with hybrid functional Becke 3-parameter Lee–Yang–Parr (B3LYP) and a basis set 6-31G* were used to investigate the structural and electronic properties of the resulting nanotubes. The stability of the substitutional Ge atoms was thus studied and explained in terms of the binding energy per dopant atom. The density of state and HOMO-LUMO gap showed that electrical conductivity increases gradually with the number of dopants. The ionization potential, electron affinity, chemical hardness and softness, and chemical potential were also calculated.