First-principles study of Si₃N₂

An investigation of the structural stability, equation of state, elastic constant, dielectric constant and band gap of Si₃N₂ was conducted using first-principles calculations. These calculations are based on density functional theory and were performed using the local density approximation and generalized gradient approximation. The structural instabilities were investigated by computing the phonon frequency to check for imaginary modes. Si₃N₂ is dynamically unstable at the pressure of around 20 GPa but mechanically stable at the same pressure. At ambient pressure, Si₃N₂ has a high dielectric constant, a modest bulk modulus of about 149 GPa and a predicted band gap of 1.05 eV and 1.19 eV using the hybrid functionals as proposed by Heyd-Scuseria-Ernzerhof, as well as the modified Becke-Johnson potential.