MD Simulation of Structural and Mechanical Transformation of Single-Walled Carbon Nanotubes Under Pressure

We investigate the structural and mechanical properties of single-walled carbon nanotubes(SWNTs)under hydrostatic pressure,using constant-pressure molecular dynamics(MD)simulations.We observed that all the SWNTs,independent of their size and chirality,behave like a classical elastic ring exhibiting a buckling transition transforming their cross-sectional shape from a circle to an ellipse.The simulated critical transition pressure agrees well with the prediction from continuum mechanics theory,even for the smallest SWNT with a radius of 0.4nm.Accompanying the buckling shape transition,there is a mechanical hardness transition,upon which the radial moduli of the SWNTs decrease by two orders of magnitude.Further increase of pressure will eventually lead to a second transition from an elliptical to a peanut shape.The ratio of the second shape transition pressure over the first one is found to be very close to a constant of∼1.2,independent of the tube size and chirality.