Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag an...Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag and armchair nanotubes there are two nonequivalent bond lengths. One bond stretches from that of the graphene sheet, while the other shrinks. Small variations on bond angles are also shown. Energy bands are calculated for the optimized structures. It is found that the intrinsic curvature of the very small nanotube greatly modifies the energy band which can no longer be well described in the tight-binding zone-folding picture. In our calculation very small nanotubes are metallic. The energy per atom fits quite well with the relation of E(R) = E0 + f/R2 even for the extreme small radius. The implications of the results on the properties of small nanotubes are discussed.展开更多
A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows...A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows the crystal to relax fully.Furthermore,the effect of pressure on the crystal structure is explicitly given in this approach.As an example,the evolution process of cobalt from a structure far from the final one to the ideal hexagonal close packing structure was given.展开更多
基金Supported by the National Key Projects of Basis Research under Grant Nos.G1999064509 and G1999032801Chinese Academy of Sciences under Grant No.KJCX2-W5-1.
文摘Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag and armchair nanotubes there are two nonequivalent bond lengths. One bond stretches from that of the graphene sheet, while the other shrinks. Small variations on bond angles are also shown. Energy bands are calculated for the optimized structures. It is found that the intrinsic curvature of the very small nanotube greatly modifies the energy band which can no longer be well described in the tight-binding zone-folding picture. In our calculation very small nanotubes are metallic. The energy per atom fits quite well with the relation of E(R) = E0 + f/R2 even for the extreme small radius. The implications of the results on the properties of small nanotubes are discussed.
基金Supported by the National Natural Science Foundation of China under Grant No.69525409,and by the Chinese Outstanding Young Investigator Foundation by the Chinese Academy of Sciences.
文摘A new molecular-dynamics method at constant pressure has been proposed.As the three edge vectors of a crystal cell as well as the position vectors of all particles are taken as independent variables,this method allows the crystal to relax fully.Furthermore,the effect of pressure on the crystal structure is explicitly given in this approach.As an example,the evolution process of cobalt from a structure far from the final one to the ideal hexagonal close packing structure was given.
