Vibrational properties of single-walled silver nanotubes studied from first principles

Abstract

The vibrational modes, especially the radial breathing modes (RBMs), of the single-walled silver nanotubes (SWSNTs) have been calculated by the first principles calculations. It is found that (1) the tip-suspended Ag (4,2) and Ag (6,3) tubes can also be potentially realized in future experiments, due to existence of a local minimum in the cohesive energies and string tension variation with their unit cell lengths. (2) The maximal frequencies of the SWSNTs are comparable to those of bulk silver, but its vibrational density of states is quite different. (3) Although the RBM frequencies of the SWSNTs depend on both of their tube diameters and chiral symmetries, they still approximately follow a linear variation law with the inverse tube diameters. (4) By investigating the stiffness coefficient of Ag (4,4) and Au (4,4) tubes, we have found that the Ag–Ag bond is stronger than the Au–Au ones. (5) The calculated first-order resonant Raman spectra are found to be sensitive to the chiral indices of SWSNTs, which may be useful in future experiment.