Energetics and electronic properties of twisted single-walled carbon nanotubes

We perform a systematic first-principles study of energetics and electronic properties of chiral carbon nanotubes (CNTs) in the density-functional theory. It is found that chiral CNTs possess slightly twisted ground-state geometries. Moderate-diameter CNTs show twisting-dependent electronic properties well classified by their chiral indices, while the electronic structures of small-diameter CNTs possess sizable but individually different twisting dependences, leading to metal-semiconductor transitions in some CNTs. The CNT having the widest fundamental gap is predicted to be the twisted (4,3) CNT.