First‐Principles Calculations to Investigate the Refractive Index and Optical Dielectric Constant of Na₃Sb<i>X</i>₄ (<i>X</i> = S, Se) Ternary Chalcogenides

Ternary chalcogenides are promising candidate for visible light absorber as they have excellent optoelectronic properties. The ternary chalcogenides Na 3 Sb X 4 ( X = S, Se) are investigated by using first‐principles calculations based on density functional theory (DFT). These chalcogenides have direct bandgap. The upper valence bands are predominantly composed of S or Se p ‐orbitals and lower conduction bands consist of hybridization between Sb and S or Se p ‐orbitals electrons. The optical absorption is investigated by calculating dielectric functions, refractive index, and optical dielectric constant. Our results of electronic and optical properties suggest potential of superionic conductors and energy storage applications.