Electrical structures and optical properties of β-Si3N4 have been calculated by means of plane wave pseudo-potential method (PWP) with GGA. The results such as lattice constants and band structures are in good agreement with experimental data. Furthermore, the pressure-dependent coefficient and band gap of β-Si3N4 have also been calculated, which will be helpful in the application of Si3N4 under high pressure.

The pressure-dependent electronic structure and physical properties of γ- Si3N4 have been calculated by means of plane wave pseudo-potential method (PWP) using GGA-PW91. Based on the calculations, we analyzed the influence of pressure on the optical and mechanical properties γ-Si3N4, which indicates that γ-Si3N4 is quite suitable for applications under high pressure.