Triclinic CdSiO3 structural, electronic, and optical properties from first principles calculations

Quantum ab initio simulations were carried out to study the CdSiO3 triclinic crystal. Unit cell parameters and atomic positions were optimized to find a minimum total energy within the density functional theory (DFT) formalism in both the local density and generalized gradient approximations, LDA and GGA, respectively. Analysis of the Kohn-Sham electronic band structure shows that there are two very close indirect band gaps Eg(Z → Γ) = 2.57 eV (2.79 eV) and Eg(Q → Γ) = 2.59 eV (2.81 eV) for the GGA-PBE (LDA-CAPZ) computations, and a direct band gap Eg(Γ → Γ) = 2.57, 2.63 eV (2.85 eV). Effective masses for holes and electrons were estimated by parabolic fitting along different directions at the valence band maximum and conduction band minimum, and they are very anisotropic. A comparison with previously reported data for triclinic CaSiO3 (wollastonite) using the LDA-CAPZ exchange-correlation functional reveals that the substitution of calcium by cadmium changes the localization of the valence band maximum in reciprocal space and decreases the band gap energies. Optical properties (dielectric function, optical absorption) for incident light polarized along different crystalline planes were computed, the optical absorption for incident light with polarization along the 0 1 0 crystalline plane being the smallest for energies near the main band gap due to the spatial disposition of the SiO4 tetrahedra and CdO6 octahedra chains that build up the structure of triclinic CdSiO3.