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

Abstract

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. 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.