Cyclacenes and short zigzag nanotubes with alternanting Ge―C bonds: theoretical impacts of Ge on the ground state,strain, and band gap

6]_n Cyclacenes and short zigzag 6]_n carbon nanotubes (n = 5–10) have unstable singlet open‐shell (S_os) ground states. We have boosted their stability by implementing altering Ge―C bonds that acquire S_cs ground states with larger band gap (ΔE_LUMO–HOMO) at B3LYP and BPW91 levels of theory. Fascinatingly, homodesmic calculations indicated release of almost two folds of strain energy upon substitution of germanium for carbon. This may turn the green lights for synthesis of germanium–carbon cyclacenes and short zigzag nanotubes. Copyright © 2014 John Wiley & Sons, Ltd.