Comprehensive computational analysis for exploring physical properties of mechanically robust metal chalcogenides...

It is essential nowadays to investigate some unique and appropriate material for the purpose of optoelectronic applications. In the current study, the structural, optoelectronic, vibrational, mechanical, magnetic, and thermodynamic properties of MLaS (M = Ag, Au) in monoclinic phase are explored. The lattice parameters (Å) for AgLaS are noted to be a = 7.28, b = 7.31, and c = 6.93, whereas for AgLaS, a = 7.61, b = 7.31, and c = 6.93 with the lattice angles of α = γ = 90 and β = 98.74 for both materials. These compounds are categorized as semiconductor due to the direct energy band gap of 1.234 eV and 0.507 eV for AgLaS and AuLaS using PBE-GGA and 1.611 eV and 0.899 eV for AgLaS and AuLaS using HSE06 functional, respectively. Interestingly, these materials unveil non-magnetic and brittleness while possessing anisotropic behavior for various magnetic and mechanical applications. Also, these chalcogenides manifest a notable rise in absorptivity and optical conductivity in the IR energy region. The existence of imaginary frequencies implies that their few vibrational modes are inherently unstable upon thermal activation. Whereas, the negative Gibbs free energy endorses thermodynamic stability. The present research is the first computational effort entrusted for MLaS (M = Ag, Au) that may offer assistance to future researchers for synthesizing these materials for optoelectronic applications.

The properties are investigated by the first principles study relying on density functional theory (DFT). These computations use norm-conserving pseudopotential approach where HSE06 functional is appraised in the framework of CASTEP code. The HSE06 functional is systematically utilized to calculate better electronic band gap and obtain correct contribution from d/f electronic states. To seek mechanical stability, Born's stability criterion is used, and the elastic parameters are computed while using Voigt-Reuss-Hills approximation. The density functional perturbation theory (DFPT) is used to examine the vibrational properties. Finally, the Harmonic Approximation technique is employed to determine thermodynamic properties.