Structural, elastic, electronic, and optical properties of NaAlSi₃O₈ and Al₄[Si₄O₁₀](OH)₈ from first-principles calculations

Context: Based on the first-principles calculations, this paper investigates the structural, elastic, electronic, and optical properties of albite and kaolinite, respectively. It is determined that both of them show structural stability, mechanical stability, and brittleness by calculating formation enthalpy, phonon dispersion, elastic, and mechanically relevant properties. Both materials are insulators with an indirect bandgap. By calculating the TDOS and PDOS, the main characteristics of the electronic structure of NaAlSi₃O₈ come from O-2p and Si-3p states, O-2p, and Al-3p states hybridization, similar to Al₄[Si₄O₁₀](OH)₈. The covalence of Si–O bonds in NaAlSi₃O₈ is greater than Al–O bonds, and the covalent property sequence of Si–O bands in NaAlSi₃O₈ is Si2-O3 > Si1-O4 > Si2-O2 > Si1-O8 > Si1-O6 > Si3-O2 > Si3-O4. The optical anisotropy of NaAlSi₃O₈ and Al₄[Si₄O₁₀](OH)₈ is analyzed. Methods: First-principles density functional theory (DFT) calculation was carried out by the CASTEP computer program. The GGA-PW91 exchange–correlation was used. The energy convergence tolerance, the maximum force, and the maximum displacement were set in the calculation.