Hydrostatic pressure effects on the structural and electronic properties of carbon nanotubes

We study the structural and electronic properties of isolated single‐wall carbon nanotubes (SWNTs) under hydrostatic pressure using a combination of theoretical techniques: Continuum elasticity models, classical molecular dynamics simulations, tight‐binding electronic structure methods, and first‐principles total energy calculations within the density‐functional and pseudopotential frameworks. For pressures below a certain critical pressure P c , the SWNTs' structure remains cylindrical and the Kohn–Sham energy gaps of semiconducting SWNTs have either positive or negative pressure coefficients depending on the value of ( n , m ), with a distinct “family” (of the same n – m ) behavior. The diameter and chirality dependence of the pressure coefficients can be described by a simple analytical expression. At P c , molecular‐dynamics simulations predict that isolated SWNTs undergo a pressure‐induced symmetry‐breaking transformation from a cylindrical shape to a collapsed geometry. This transition is described by a simple elastic model as arising from the competition between the bond‐bending and PV terms in the enthalpy. The good agreement between calculated and experimental values of P c provides a strong support to the “collapse” interpretation of the experimental transitions in bundles. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)