▎ 摘　　要

This paper explores the stability and physical properties of double-walled carbon nanotubes and the bilayer graphene obtained from their unfolding. It can be found that the stability is almost unchanged within a certain range of diameter of the double-walled carbon nanotubes. As the diameter of the carbon nanotubes increases to around 27.798 angstrom, the rising average atomic energy indicates a decrease in their stability. The smallest diameter group in the zigzag-shaped DWCNT has the lowest energy and the highest stability, while the largest diameter group of armchair-shaped nanotubes has the highest energy and the worst stability. Single-walled carbon nanotubes have a tendency to metallize when combined into double-walled carbon nanotubes. The metallization trend of carbon nanotubes is influenced by the tube diameter and chiral index: as the tube diameter increases, its curvature becomes smaller and the potential difference increases, and the metallization trend becomes more pronounced. As the curvature decreases to zero, the semiconducting double-walled carbon nanotubes turn into metallic bilayer graphene as the surface gradually flattens out. However, by unfolding the (18,0)@(27,0) zigzag-shaped carbon nanotubes, which originally have metallic properties, the resulting graphene has semimetallic properties. Usually, pi-bonds play a role in the interlayer coupling of bilayer graphene structures and double-walled carbon nanotube structures. Therefore, as the curvature decreases, the pi-bonding of the carbon nanotubes increases the binding energy of the two layers. This further explains the nanotube unfolding leading to metallization. With the exception of the group (18,0)@(27,0), the electrons are mainly concentrated in the outer tube and the inner layer is almost completely depleted. During the unfolding process, electrons migrate toward the inner tube, arriving at the inner layer as the curvature approaches zero. So this bilayer graphene obtained by (18,0)@(27,0) double-walled carbon nanotube unfolding does not have metallicity.