Structural and electronic properties of carbon nanotubes under hydrostatic pressures

We studied the structural and electronic properties of carbonnanotubes under hydrostatic pressures based on molecular dynamicssimulations and first principles band structure calculations. It isfound that carbon nanotubes experience a hard-to-soft transition asexternal pressure increases. The bulk modulus of soft phase is twoorders of magnitude smaller than that of hard phase. The bandstructure calculations show that band gap of (10, 0) nanotubeincreases with the increase of pressure at low pressures. Above acritical pressure (5.70GPa), band gap of (10, 0) nanotube dropsrapidly and becomes zero at 6.62GPa. Moreover, the calculated chargedensity shows that a large pressure can induce an{sp}²-to-{sp}³ bonding transition, which is confirmed byrecent experiments on deformed carbon nanotubes.