In this paper,a novel double-wall carbon nanotube（DWCNT） with both edge and screw dislocations is studied by using the molecular dynamics（MD） method.The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9,respectively,by taking into account the symmetry,integrality,and thermal stability of the composite structures.It is found that melting first occurs near the dislocations,and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K-2700 K.At the premelting temperatures,the shrink of the dislocation loop,which is comprised of edge and screw dislocations,implies that the composite dislocation in DWCNTs has self-healing ability.The dislocated DWCNTs first fracture at the edge dislocations,which induces the entire break in axial tensile test.The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs.Our results not only match with the dislocation glide of carbon nanotubes（CNTs） in experiments,but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope（HRTEM）,which is deemed to cause the motion of dislocation loop.
In this paper, we quantitatively study the quantum diffusion in a bilateral doped chain, which is randomly doped on both sides. A tight binding approximation and quantum dynamics are used to calculate the three electronic characteristics： autocorrelation function C（t）, the mean square displacement d（t） and the participation number P（E） in different doping situations. The results show that the quantum diffusion is more sensitive to the small ratio of doping than to the big one, there exists a critical doping ratio qo, and C（t）, d（t） and P（E） have different variation trends on different sides of qo. For the self-doped chain, the doped atoms have tremendous influence on the central states of P（E）, which causes the electronic states distributed in other energy bands to aggregate to the central band （E = 0） and form quasi-mobility edges there. All of the doped systems experience an incomplete transition of metal-semiconductor-metal.
