<i>Ab initio</i>structural, elastic, and vibrational properties of carbon nanotubes

TLDR

The study uses ab initio calculations to investigate the structural, elastic, and vibrational properties of single‑wall carbon nanotubes across various radii and chiralities. The authors employ pseudopotential‑density‑functional theory to compute these properties for large‑cell nanotubes, monitoring their dependence on radius and comparing the results with zone‑folding predictions and phonon branch behavior. They find that Young’s modulus and Poisson ratio largely match graphite values, with only minor radius‑dependent deviations, while curvature‑induced rehybridization causes small deviations at small radii; phonon branches exhibit slight chirality dependence, and the zone‑folding approximation remains accurate except in low‑frequency regions.

Abstract

A study based on ab initio calculations is presented on the structural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities. These properties are obtained using an implementation of pseudopotential-density-functional theory, which allows calculations on systems with a large number of atoms per cell. Different quantities are monitored versus tube radius. The validity of expectations based on graphite is explored down to small radii, where some deviations appear related to the curvature-induced rehybridization of the carbon orbitals. Young moduli are found to be very similar to graphite and do not exhibit a systematic variation with either the radius or the chirality. The Poisson ratio also retains graphitic values except for a possible slight reduction for small radii. It shows, however, chirality dependence. The behavior of characteristic phonon branches as the breathing mode, twistons, and high-frequency optic modes, is also studied, the latter displaying a small chirality dependence at the top of the band. The results are compared with the predictions of the simple zone-folding approximation. Except for the known deficiencies of the zone-folding procedure in the low-frequency vibrational regions, it offers quite accurate results, even for relatively small radii.