Metastability of multitwinned Ag nanorods: Molecular dynamics study

Nanoscale rods have been shown to exhibit a multiple twinned structure. The rods grow along a [110]-type crystallographic direction and have a pentagonal cross section with five (111) twins connecting the wire center to the corners of the pentagon. Here, we use molecular dynamics simulations with an embedded atom method interatomic potential for Ag to compute the ground-state energies of the multitwinned rods and compare with the bulk equilibrium crystal shape, as estimated from a Wulff construction. The excess energy of the nontwinned equilibrium nanorods and the multitwinned nanorods was obtained as a function of the wire length (L) as well as the cross sectional area (Acs). Various contributions to the total energy, such as twin boundary energy and surface energies, are discussed and included in an analytical model that compares favorably with the simulation results. Our results show that for infinitely long nanowires with Acs<1500 nm2, the nontwinned structure is always energetically favorable. However, if the energy of the dipyramidal atomic structure at the nanorod ends is included in the model then the twinned nanorods are stable with respect to the nontwinned rods below a critical aspect ratio (L/ Acs ).