  Density functional methods have been used to calculate the electronic
properties of aligned smalldiameter single-walled carbon nanotubes under
hydrostatic pressures. Abrupt pressure induced semiconductor-metal and
metal-semiconductor transitions concomitant with changes in structure are
observed. Novel and unexpected unit cell nanotube cross-sections are found.
These tubes are observed to form interlinking structures at very high
pressures. The large changes in electronic structure and the ability of
different small diameter nanotubes to respond in different pressure regimes
suggest their use in high pressure multiple switching devices.
