Hydrostatic Pressure Effects on the Structural and Electronic Properties of Carbon Nanotubes

TL;DR

This paper investigates how hydrostatic pressure affects the structure and electronic properties of single-wall carbon nanotubes using various theoretical methods, revealing a pressure-induced collapse transition and family-dependent electronic behavior.

Contribution

It combines multiple theoretical techniques to analyze pressure effects on SWNTs, providing a unified understanding of structural transitions and electronic property changes under pressure.

Findings

SWNTs remain cylindrical below a critical pressure P_c

Electronic energy gaps show family-dependent pressure coefficients

SWNTs undergo a symmetry-breaking collapse at P_c

Abstract

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.