Raman modes of the deformed single-wall carbon nanotubes

With the empirical bond polarizability model, the nonresonant Raman spectra of the chiral and achiral single-wall carbon nanotubes (SWCNTs) under uniaxial and torsional strains have been systematically studied by ab initio method. It is found that both the frequencies and the intensities of the low-frequency Raman-active modes almost do not change in the deformed nanotubes, while their high-frequency part shifts obviously. Especially, the high-frequency part shifts linearly with the uniaxial tensile strain, and two kinds of different shift slopes are found for any kind of SWCNTs. More interestingly, Raman peaks are found in the nonresonant Raman spectra under torsional strain, which are explained by (a) the symmetry breaking and (b) the effect of bond rotation and the anisotropy of the polarizability induced by bond stretching.