Structural, elastic, electronic, and optical properties of NaAlSiO and Al[SiO](OH) 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 NaAlSiO come from O-2p and Si-3p states, O-2p, and Al-3p states hybridization, similar to Al[SiO](OH). The covalence of Si-O bonds in NaAlSiO is greater than Al-O bonds, and the covalent property sequence of Si-O bands in NaAlSiO is Si2-O3 > Si1-O4 > Si2-O2 > Si1-O8 > Si1-O6 > Si3-O2 > Si3-O4. The optical anisotropy of NaAlSiO and Al[SiO](OH) 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.