Low temperature study of the structural stability, electronic and optical properties of the acanthite α-Ag2S: Spin-orbit coupling effects and new important ultra-refraction property

Abstract

This paper aims to investigate the structural and optoelectronic properties of acanthite silver sulfide using the first principles calculations and considering the spin-orbit coupling (SOC) effects on the electronic structure. The cohesive energy was calculated with the GGA potential and the results show that Ag–S is a majority covalent bond, accurately confirmed by the electron density, with an ionicity factor of 0.055–0.11. The band structure and the density of states (DOS) were computed by the GGA with and without SOC. It was found that the SOC-induced band splitting near the Fermi energy increases the gap energy from 0.87 to 0.97eV. Spin magnetic moment was determined to be 0.0003 μβ, which confirms the absence of magnetic behavior of Ag2S. Becke Johnson's modified mBJ coupled with the GGA was applied to obtain an energy gap in the experimental gap vicinity. Finally, the optical properties were calculated in detail by applying the scissor operator where important maximal birefringence was found to be 0.34 for Ag2S in the non-absorbing region which allows it to be a promoter material for non-linear optics. In addition, several new optical properties of Ag2S were determined; Ag2S theoretically has a high static dielectric constant that becomes an important ultra-refractive material in the UV-C spectrum for future photonic applications.