Prediction of phonon properties of 1D polyatomic systems using concurrent atomistic-continuum simulation

In this work, we present the simulation results of phonon properties, including phonon dispersion relations, group velocities, phonon relaxation time and mode-specific thermal conductivity, of low-dimensional crystals using the newly developed concurrent atomistic-continuum (CAC) method. With significantly less number of degrees of freedoms than all-atom molecular dynamics, the CAC method predicts the phonon properties of one-dimensional (1D) polyatomic crystals at finite temperatures with the full anharmonicity of the atomic interactions being incorporated. Complete phonon branches of polyatomic crystals are obtained by CAC through the phonon spectral energy density analysis. It is shown that CAC allows medium to long-wavelength phonon transport from atomic to coarsely meshed finite element region without the need of special numerical treatment. The frequency-dependent phonon group velocities are explicitly measured in the simulation. Sub-THz phonon lifetimes in 100 -mm-long polyatomic chains containing 400 million of atoms are predicted. Analysis of the phonon mode-specific thermal conductivity shows that the medium to long-wavelength acoustic phonons are contributing to the majority of the heat transport in 1D crystal, suggesting that the long-wavelength phonons effectively act as thermal carriers in 1D system. This work provides a possible explanation for the anomalous heat transport observed in low-dimensional materials.