Lattice dynamics of twisted ZnO nanowires under generalized Born-von Karman boundary conditions

Due to their excellent structural flexibility, low dimensional materials allow to modulate their properties by strain engineering. In this work, we illustrate the phonon calculation of deformed quasi-one dimensional nanostructures involving inhomogeneous strain patterns. The key is to employ the generalized Born-von Karman boundary conditions, where the phonon states are characterized with screw and rotational symmetries. We use wurtzite ZnO nanowire (NW) as a representative to demonstrate the validity and efficiency of the present approach. First, we show the equivalence between the phonon dispersions obtained with this approach and that obtained with standard phonon approach. Next, as an application of the present approach, we study the phonon responses of ZnO NWs to twisting deformation. We find that twisting has more influence on the phonon modes resided in the NW shell than those resided around the NW core. For phonon at the NW shell, the modes polarized along the NW axis is more sensitive to twisting than those polarized in the NW radial dimension. Twisting also induces significant reduction in group velocities for a large portion of optical modes, hinting a non-negligible impact on the lattice thermal conductivity. The present approach may be useful to study the strain-tunable thermal properties of quasi-one dimensional materials.