Ab initio Study of Some Physical Properties of the Cu2MgSiS4 and Cu2MgGeS4 diamond-like semiconductors and Sr2GeN2 polymorphs

Abstract

In The present work, we have explored some physical properties of the two newly synthetized quaternary diamond-like semiconductors Cu2MgSiS4 and Cu2MgGeS4, and two polymorphs of the ternary nitrides α-Sr2GeN2 and β-Sr2GeN2, using firstprinciple calculations based on the density functional theory (DFT). The exchange-correlation effects were treated within the new version of the generalized gradient approximation (GGA-PBEsol). The structural, elastic, electronic and optical properties of the two considered diamond-like semiconductors were studied in detail using two complementary first-principles approaches: the pseudopotential plane wave (PP-PW) and the full potential augmented plane wane (FP-LAPW). The calculated equilibrium structural parameters are in good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties, including elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature, were predicted. We find that the inclusion of the electronic exchange-correlation through the newly developed TB-mBJ improves the description of the electronic structure. The TB-mBJ yields a direct band gap (Γ-Γ) of 2.64 and 1.54 eV for Cu2MgSiS4 and Cu2MgGeS4, respectively. Frequency-dependence of the dielectric function, refractive index,extinction coefficient, absorption coefficient, reflectivity, energy loss function and optical conductivity were predicted, and the origins of the observed electronic transitions were assigned. Both Cu2MgSiS4 and Cu2MgGeS4 exhibit noticeable absorption in the ultraviolet range.