Abstract
The pentagon-heptagon (5/7) pair in a zigzag single-walled carbon nanotube (SWCNT) is described as a dislocation by the modified Peierls-Nabarro (P-N) theory. The theory takes discrete effects, size effects and curvature effects into account. The bonds variation and shape distortion caused by 5/7 pair have been evaluated. It is found that the neck bond (shared bond) becomes longer while the shoulder bonds become shorter comparing with the one of the hexagons. The results show that the zigzag chain across the center of the 5/7 pair will bend slightly in the axis direction towards the heptagon, and the tube will be flattened where the 5/7 pair is located because of the appearance of the internal stress and nonzero curvature.