Modeling double-helix carbon chains inside single-walled carbon nanotubes: Stable structures and XRD analysis

Atomic models are applied to investigate quasi-one-dimensional composites. The study presents the theoretical prediction of stable double-helix carbon chains growing inside single-walled carbon nanotubes as a function of tube radius. Meanwhile, our analysis shows that metastable structures may co-existence with the stable one, for small tubes. The classical molecular dynamics simulation shows that the regular and distorted double-helix C-chains are obtained with the tube's diameter smaller and larger than 13.32 Å, respectively. The temperature plays a minor role in the stable carbon chain structure unit it increases to 2500 K. The geometry optimization and the electronic structural analysis of the obtained optimal structure by the DFT calculation further justify our classical force field analysis. The electronic structure of SWCNTs can be significantly modified by the inserted carbon chain. The orbital hybridization between the host-guest molecules plays a key role in stabilizing the encapsulated double-helix carbon chain. Finally, X-ray powder diffraction (XRD) patterns of stable helical structures inside armchair tubes are presented for guidance of future experimental analyses.