First-principles study of vibrational and dielectric properties ofβ−Si3N4

First-principles calculations have been conducted to study the structural, vibrational, and dielectric properties of $\beta \text{−}{\mathrm{Si}}_3{\mathrm{N}}_4$. Calculations of the zone-center optical-mode frequencies (including longitudinal-optical/transverse-optical splittings), Born effective charge tensors for each atom, and dielectric constants, using density functional perturbation theory, are reported. The fully relaxed structural parameters are found to be in good agreement with experimental data. All optic modes are identified and agreement of theory with experiment is excellent. The static dielectric tensor is decomposed into contributions arising from individual infrared-active phonon modes. It is found that high-frequency modes mainly contribute to the lattice dielectric constant.