Strain-induced Raman-mode shift in single-wall carbon nanotubes: Calculation of force constants from molecular-dynamics simulations

Abstract

The force-constant calculation based on molecular-dynamics simulations is carried out to investigate the effect of axial strain on the Raman modes of $(n,n)$ and $(n,0)$ single-wall carbon nanotubes. It is found that the frequencies of both radial breathing mode (RBM) and tangential modes (TMs) upshift in compression but downshift in tension. Especially, a sharp reduction in the RBM occurs when the tubes buckle under compression. More interestingly, the critical strain of RBM is inversely proportional to the tube diameter and also depends on the tube chirality. Moreover, three TMs present two different kinds of slopes with axial strain, which can be assigned to the experimentally measured ${G}^{+}$ and ${G}^{\ensuremath{-}}$ peaks. TMs change trends with strain satisfactorily agree with the experimental results. Under compression, the results are valuable to understand the effect of axial strain on tubes under nonhydrostatic pressure.