Carbon Nanotubes under Hydrostatic Pressure: The Deformation Transition

Isolated single-wall carbon nanotubes (SWNTs) deform from their usual cylindrical shape to a collapsed or oval cross-section upon increase of hydrostatic pressure. We use classical molecular-dynamics simulations to study the structural properties of isolated SWNTs under pressure near this deformation transition. Within our model, we find two distinct behaviors depending on the nanotube diameter $d$. For $d > d_c \approx 12$ \AA, SWNTs collapse from a circle to a peanut or racetrack cross-section at a critical pressure $P_c$ with a discontinuous change in volume. The van der Waals interactions between the opposite walls of the tube play a crucial role in driving this discontinuous transition. For a range of pressures, both circle and collapsed cross-sections are locally stable and the system shows hysteresis. For $d < d_c$, the transition is continuous, from a circle to an oval cross-section. RBC acknowledges financial support from the John Simon Guggenheim Memorial Foundation and Brazilian funding agencies CNPq, CAPES, FAPERJ, Instituto de Nanoci{\^e}ncias, FUJB-UFRJ and PRONEX-MCT. This work was supported by NSF Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. DOE under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NERSC and NPACI.