Ab Initio Study of the Relative Stability and Opto-Electronics Properties of the Cu2MgSiS4 Compound

The ab initio calculations based on density functional theory were performed to study structural, elastic, and opto-electronic properties of the Cu2MgSiS4 compound in three zinc-blende derived and one wurtzite derived structures. These calculations are carried out using the full potential linear augmented plane wave plus local orbital method, implemented into the WIEN2k computer code. Within generalized gradient approximation based on the revised Perdew-Burke-Ernzerhof exchange-correlation density functional the optimized lattice parameters and atomic positions are found to be in a good agreement with available experimental values. The total energies, obtained at equilibrium of this compound in four phases, reveal that both stannite and wurtzite-stannite are the most energetically favorable structures whereas the kesterite structure remains energetically probable under ambient conditions. The mechanical stability of this compound in these three phases is examined and established. Moreover, several isotropic elastic moduli were estimated via the calculated single crystalline elastic constants. In particular, our results show that this compound in these structures could be classified as ductile material and the highest elastic anisotropy were demonstrated by WS structure. On the other hand, the calculations of the electronic structure and optical properties were performed at the Perdew-Burke-Ernzerhof exchange-correlation density approximation level, improved by the Tran-Blaha modified Becke-Johnson potential to give an enhanced depiction of the band-gap energies and optical spectra. The fundamental band gap for the WS phase is calculated to be 2.44 eV. Analysis of the electronic structure reveals that the Cu(3d)-S(3p) hybridized antibonding state forms the valence band edge, while the conduction band edge is composed of the Si(3s)-S(3p) hybridized antibonding state. The optical response of the material in the visible and ultraviolet range is determined by calculating its complex dielectric tensor. It was observed that this compound in these three phases does not exhibit a large optical anisotropy. The estimated optical band gap 3.10 eV for WS phase is found to be in much closer agreement with the experimental findings. Over all, the obtained results seem to be more reliable compared to previous reported calculations and with available experimental results.