▎ 摘　　要

Molecular dynamics simulations for graphene flakes of various shapes are performed. The equilibrium structures of graphene flakes are obtained. Round, hexagonal, and rectangular graphene flakes are dealt with, and their sizes are varied from a few angstroms to 200 A degrees. It is shown that for round and hexagonal graphene flakes of small size, the edge configuration influences their energy in equilibrium. Graphene nanoribbons (GNRs) of various aspect ratios are equilibrated at low temperature. The energies of the equilibrated graphene flakes with zigzag (ZZ) edges are lower than the energies of the equilibrated graphene flakes with armchair (AC) edges. This result corresponds to the scanning tunneling microscopy observations in the literature. The atomic bonds on the edges of graphene flakes with both edge configurations are reconstructed. The bond lengths of such reconstructed edges are smaller than the lengths of the atomic bonds inside them. Therefore, free graphene flakes undergo compressive edge stress and vibrate at finite temperature. Constrained GNRs also vibrate, and the amplitudes of the vibrations of the GNRs with ZZ edges are smaller than those of the GNRs with AC edges. On designing and fabricating GNR devices, GNRs with ZZ edges are more favorable than GNRs with AC edges, and vibrations of GNRs should be taken into account.