Structural, Elastic, Electronic and Optical Properties of LaOAgS-Type Silver Fluoride Chalcogenides: First-Principles Study

First-principles density functional calculations were performed to investigate the structural parameters, elastic moduli and related properties, electronic band structure and optical properties of three LaOAgS-type barium silver fluoride chalcogenides BaAgChF (Ch denotes the chalcogenides S, Se and Te). The calculated structural parameters are in good accordance with the existing experimental data. The single-crystal and polycrystal elastic moduli were determined via the strain-stress technique. The investigated compounds show a strong anisotropic behaviour of the structural and elastic parameters. The calculated electronic band structure using the Tran-Blaha modified Becke-Johnson potential reveals that the three considered systems are large direct band gap semiconductors. The assignments of the energy band electronic states and chemical bonding character were accomplished with the help of the l-decomposed atomic densities of states diagrams. Frequency-dependent polarized optical functions were computed for an energy range from 0 eV to 30 eV. The microscopic origin of the electronic states that is responsible for the optical spectra structures were determined. The optical spectra exhibit a considerable anisotropy. Several trends in the variation of the considered physical properties with the atomic number Z of the chalcogenide Ch element in the BaAgChF series are observed.