First-principles Study On The Morphology Of Carbon Nanotubes On Co-based Mixed Clusters

Since the discovery of carbon nanotubes,the study of carbon nanotubes and related systems has become an important frontier research field in nanomaterials research.Carbon nanotubes have great potential application value in a range of fields,such as composites、hydrogen storage and catalysis,because of their high strength,low density and hollow properties,which make carbon nanotubes exhibit excellent mechanical,heat,and electromagnetic properties.Single-walled carbon nanotubes（SWCNT）structure is relatively simple,theoretical research is relatively easy.Because of the difference between size（diameter）and symmetry（chirality）,different single-walled carbon nanotubes have different conductivity characteristics（metallic or semiconducting）,which makes single-walled carbon nanotubes have their important significance and application value in nano-electronic devices.Computer simulation provides a good way to describe and control the growth of carbon nanotubes at the atomic level scale,so that we can understand the specific kinetic behavior of carbon nanotubes growing at the atomic level by computer simulation.This paper mainly does the following two aspects:（1）The lowest-energy geometrical and electronic structures of Cu₃₈ cluster are investigated by density-functional calculations combined with a genetic algorithm based on a many body semi-empirical interatomic potential,the traditional FCC-truncated Octahedron（OH）and an incomplete-Mackay icosahedron（IMI）are recognized as the two lowest energy structures（energetically degenerate isomers）but with different electronic structures:a semiconductor-type with the energy-gap of0.356 eV for the IMI and a metallic-type with negligible gap for the OH,which is in good agreement with the experimental results.The electron affinity and ionization potential of Cu₃₈ are also discussed and compared with the observations of the ultraviolet photoelectron spectroscopy experiments.The dynamical isomerization of the OH-like and IMI-like structures of Cu₃₈ is revealed to dominate the pre-melting stage through the investigation by the molecular dynamics annealing simulations.（2）Based on the basic structural motif of the icosahedral Co₅₅ clusters,the interaction between the Co-Mo clusters with the Mo atom（s）at different substitution（doping）sites and single-walled carbon nanotubes with different chirality（10,0）and（5,5）was studied by density functional theory.The results show that the interaction between Co-Mo mixed cluster system and single-walled carbon nanotubes is closely related with the location（internal or surface）of the doped Mo atom（s）in clusters and the chirality（symmetry）of the single-walled carbon nanotubes.Compared with pure Co₅₅ clusters,Mo atom doped clusters have obvious enhanced structure control effect on single-walled carbon nanotubes,which has enlightenment for the controllable synthesis of single-walled carbon nanotubes.