Pressure-induced hard-to-soft transition of a single carbon nanotube

We demonstrate a hydrostatic pressure-induced hard-to-soft transition of an isolated single wall carbon nanotube, using classical and ab initio constant-pressure molecular-dynamics simulations and continuum elastic theory analysis. At low pressure, the carbon tube is hard. Above a critical pressure, the tube becomes much softer with a decrease of bulk modulus by two orders of magnitude. The hard-to-soft transition is caused by a pressure-induced shape transition of the tube cross section from circular to elliptical.