单向压力对碳纳米管(6, 6)晶体电子结构的影响

通过第一性原理计算研究了垂直于碳纳米管轴向的单向压力对碳纳米管(6，6)晶体电子结构特性的影响.计算研究发现：由碳纳米管(6，6)组成的四方结构晶体(t相)具有金属特性，电子可以沿碳纳米管管壁运动；在单向压力作用下,t相发生结构相变形成非成键相，随着压力的进一步增大，碳纳米管间产生键合，形成了成键相；单向压力对碳纳米管(6，6)晶体的能带结构影响主要表现在π能带和π^*能带，伴随着单向压力的增加，碳纳米管晶体的电学性质经历从金属到半导体再到活泼金属的转变；非成键相的电子被局域在碳纳米管附近使晶体具有半导体特性，而成键相的电子不仅可以沿着碳纳米管管壁运动，还可以在碳纳米管之间(即成键方向)运动，从而使成健相晶体具有活泼的金属特性. 关键词： 碳纳米管晶体 第一性原理计算 金属—半导体转变

The effects of the uniaxial pressure on electronic structures of the (6, 6) single-walled carbon nanotube crystal

In this paper, we performed the first-principles calculations of the effects of the uniaxial pressure on electronic structures of the (6, 6) single-walled carbon nanotube crystal (SWNTC). The applied pressure is perpendicular to the axis of carbon nanotubes. The calculated results show that the (6, 6) SWNTC with tetragonal structure (t phase) is metallic, and its electrons can move along the walls of carbon nanotubes. With the increasing of the uniaxial pressure, the (6, 6) SWNTC undergoes the structural phase transitions, and transforms from the t phase to the unbonded phase, and then to the bonded phase. The uniaxial pressure mainly affects the π and π^* bands of the band structure of the (6, 6) SWNTC, and these effects on the bands are not only in k_xk_y plane but also in the direction of k_z. The electronic properties of the crystal can alter from metal to semiconductor, then to metal again as the uniaxial pressure increases. The distributions of electronic charge densities show that electrons of the unbonded phase are localized near the carbon nanotubes. And electrons of the bonded phase can move not only along the walls of carbon nanotubes, but also between the two nearest nanotubes through the chemical bonds.