Structural, electronic and optical properties of ilmenite and perovskite CdSnO₃from DFT calculations

Abstract

CdSnO(3) ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at ω = 0 and ∞ were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO(3) polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO(3) does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO(3) with ferroelectric properties.

Optical and electronic properties of orthorhombic and trigonal AXO3 (A=Cd, Zn; X=Sn, Ge): First principle calculation

“…The general features of the energy bands such as band gaps, DOS and orbital hybridization are similar for all investigated compounds. Furthermore our results are in agreement with the results obtained in previous calculations [1,25,26]. We have summarized the band gap energies for ZnXO 3 and CdXO 3 in Table 1 with the available theoretical and experimental results.…”

“…The lattice parameters obtained as a result of this optimization are shown in Table 1 with the experimental and theoretical results. The structural parameters obtained are in a good agreement with the experimental and theoretical values [1,[16][17][18][19][20][21][22][23][24][25][26]. We have used these structural properties in all our subsequent calculations.…”

Vibrational and thermodynamic properties of orthorhombic CaSnO3 from DFT and DFPT calculations

“…We have also used pseudopotentials to replace the core electrons in each atomic species. The norm-conserved pseudopotentials [31], generated using the OPIUM code [32], were adopted in the GGA calculations following the same scheme of previous works [2,33,34]. The electronic valence configurations for each atomic species were: Ca3s 2 3p 6 4s 2 , Sn -5s 2 5p 2 , and O -2s 2 2p 4 .…”

“…The quality of this basis set is kept fixed as the unit cell volume varies during geometry optimization. After obtaining the optimized unit cell and atomic positions, the infrared and Raman spectra were evaluated for the optimized GGA unit cell as well as the frequencies of active modes, together with the calculated dielectric permittivity and polarizability tensors, by following the same scheme described in previous works [33][34][35]37]. Furthermore, the phonon calculations were carried out within the harmonic approximation, using the density functional perturbation theory (DFPT) calculation, or linear response formalism [27,38], to determine its dispersion and density of states.…”

Prediction of possible CaMnO3modifications using anab initiominimization data-mining approach

“…Such perovskite ! ilmenite phase transitions have been observed experimentally and theoretically in various compounds (Nancy & McMillan, 1984;Sesion et al, 2010); however, to our knowledge, no experimental or calculated data exist regarding a possible ilmenite structure type in the CaMnO 3 system.…”