First-principles study of vibrational and dielectric properties of   {\beta}-Si3N4
  First-principles calculations have been conducted to study the structural, vibrational and dielectric properties of {\beta}-Si3N4. Calculations of the zone-center optical-mode frequencies (including LO-TO splittings), Born effective charge tensors for each atom, 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. 
Yongqing Cai, Qingfeng Zeng, Litong Zhang, Laifei Cheng, Yongdong Xu
cond-mat.mtrl-sci