Structural, elastic constants, hardness, and optical properties of pyrite-type dinitrides (CN 2, SiN 2, GeN 2)
The crystal structures, band structures, elastic constants, hardness, and optical properties of pyrite-type dinitrides (CN 2, SiN 2, and GeN 2) are obtained from the density functional theory using the plane-wave pseudopotential (PWP) method within the local density and generalized gradient approximations. The formation enthalpies for AN 2 (A=C, Si, and Ge) compounds suggest the three structures that are stable. The calculated band structures show the indirect gaps ( Γ-R) in CN 2, SiN 2, and GeN 2. The intrinsic hardnesses of AN 2 (A=C, Si, and Ge ) compounds are calculated. Our results show that the cubic CN 2 and SiN 2 are superhard materials. Furthermore, we studied the optical properties such as the complex dielectric function and the electron energy loss spectra.