Molecular dynamics studies of phonon spectra in ultrathin helical multi-shell gold nanowire

The phonon spectra in 7-1 structure of gold nanowire, which is the simplest structure among possible helical multi-shell nanowire, are studied by using molecular dynamics simulations with a tight-binding many-body potential. Our simulation identifies the outer tube (shell) and inner gold-atom row (core strand) vibrational modes. Generally, atomic interactions have a stiffening force constant due to the shortening the neighbor distance in the interior atoms. The high frequency characteristics of the vibrational modes of core strand are more pronounced than that of outer shell. However, the global phonon density of states (DOS) is predominated by the outer shell modes. The results show that the vibrational frequencies of the ultrathin gold nanowires are dependent on the strain of the wire stretching. The high frequency modes gradually decrease when strain is increased.