Computational study of the structural, electronic and optical properties of M2N2(NH): M = C, Si, Ge, Sn

We present the first principles calculations of electronic, structural and optical properties of Ge2N2(NH) and Sn2N2(NH), isostructural with Si2N2(NH) and C2N2(NH). The M2N2(NH) compounds, where M = Si or C or Ge or Sn, crystallise into base-centered orthorhombic (BCO) structure, space group Cmc21. Our results indicate that Ge2N2(NH) and Sn2N2(NH) are stable compounds, satisfying mechanical stability tests and lack imaginary phonon modes. In addition, the two compounds have fairly smaller bulk moduli compared to Si2N2(NH) and C2N2(NH). Ge2N2(NH) has a direct band gap of 2.66 eV in DFT-GGA while Sn2N2(NH) posses a small indirect band gap of 1.05 eV. We also analyse the dielectric behaviours of the M2N2(NH) compounds within infrared (IR), visible and ultraviolet (UV) regimes in which Ge2N2(NH) and Sn2N2(NH) show remarkable characteristics.