Electronic, elastic, linear and nonlinear optical properties of beryllium based chalcopyrite BeMN₂ (M = C, Si): an ab-initio study

The BeCN₂ and BeSiN₂ compounds with the non-centrosymmetric chalcopyrite structure have been investigated by means of ab-initio density functional theory calculations. The electronic structures, the linear optical properties (dielectric constant, refractive index), non-linear optical quadratic (NLO) coefficients and elastic constants are calculated and commented. Moreover, birefringence phase-matching conditions for some frequencies have been examined for second harmonic generation (SHG). Indeed, BeCN₂ can double frequencies in the range between 0.2 and 1.05 eV by realizing type II phase matching, as well as it can double 1.17eV (1.064 μm) frequency to generate a green light (0.532 μm) by realizing the condition of type I phase matching with nonlinear optical coefficient d₁₄ ≈ (16 and 4.5) × (d₁₄) _KDP for (BeCN₂ , BeSiN₂ ).