Structural, phonon, mechanical, optical, and thermodynamic properties of stable β-La2S3 from first-principles calculations

Abstract

The band structures, density of states, phonon, optical properties, and thermodynamic properties of β-La2S3 were calculated from first-principles using the plane-wave pseudopotential method. First, the structures were fully relaxed through the first-principles method. Then, the zone-center phonon-mode frequencies were evaluated within the framework of density functional perturbation theory. Properties related to the structure, phonons, optics, elastic constants, and thermodynamics of β-La2S3 were reported. The dielectric function, refractive index, absorption coefficient, extinction coefficient, infrared (IR) reflectance, energy, heat capacity, and Debye temperature spectra were also given. β-La2S3 was a direct-gap semiconductor, and calculation indicated that its energy gap was 0.191 eV. From the phonon spectra, it could be concluded that the lattice dynamics were stable. A strong IR reflection occurred in a range of 0- 1000 nm, arising from several strong IR-active modes, resulting in poor transmission properties. Relatively good transmission properties were observed in the range above 2000 nm, with low reflectivity and dissipation due to the absence of IR-active or weak modes.