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Abstract Using first principles density functional theory (DFT) simulations, the structural, electronic, optical and elastic properties of CaTa 2 O 6 oxide for cubic and orthorhombic phases are studied by highly accurate (FP-LAPW) method within the GGA + U approximation. The calculated lattice parameters are consistent with available experimental data. The electronic band structure calculations have shown that the band gaps in CaTa 2 O 6 are equal to 3.08 eV and 4.40 eV for the cubic and orthorhombic structures, respectively. For both the phases the main optical properties, e.g., absorption coefficient, dielectric constant, energy loss function, reflectivity are calculated and discussed in detail in the spectral range 0–14 eV. Cubic and orthorhombic phases exhibit significantly different optical characteristics. The electronic bonding characters of CaTa 2 O 6 with different symmetries are explored via charge density distribution mapping. Strong covalent bonding character dominates in both the phases of CaTa 2 O 6. Elastic properties of CaTa 2 O 6 for cubic and orthorhombic phases are also investigated. The stress strain method is used for the determination of elastic constants in both the phases. The bulk modulus, shear modulus, Young's modulus, along with the important elastic anisotropy factors and Poisson's ratio are studied in detail. Graphical abstract Image 1 Highlights • Electronic, and optical properties of CaTa 2 O 6 in cubic and orthorhombic phases are studied. • Energy band gaps were equl to 3.08 and 4.40 eV, respectively. • Optoelectronic features are due to Ca-s, Ta-p, O-p orbitals in (c.p.), Ta-p and O-(o.p.) • The Zener factor and Poison's ratio confirm elastically anisotropic characteristics. [ABSTRACT FROM AUTHOR]

Abstract Nitrido silicates are emerged as highly efficient luminescent materials (phosphors) that found considerable industrial application as white light emitting diodes (LEDs) have been studied with respect to band structure and related electronic structure parameters. They have tunable optical properties, as the band gap is of indispensable because it determines both the electrical and optical features of the material, which can be varied by the material composition (by doping technique). It is found also that the nitride (alumo) silicates "Sr 2 Si 5 N 8 : Eu2+" have wide industrial application as highly efficient red-emitting phosphor materials in pc-LEDs. In this report we apply density functional theory (DFT) within the GGA+U approach to study the structural, electronic and optical properties of Eu2+ and Ce3+ doped Sr 2 Si 5 N 8. The total energy has been optimized as a function of the unit cell volume. Electronic structure including, the electronic density of state (DOS), the band structure and the linear optical susceptibility are calculated for the relaxed structure applying the optimized lattice constant. The calculated optical dispersion of dielectric susceptibility are closely related to the corresponding electronic structure and our results are in very good agreement with experimental data. Graphical abstract Image 1 Highlights • Complex studies of band structure for Sr 2 Si 5 N 8 and doped compound with Eu2+and Ce+3 have been done. • Static value of real part for pure Sr 2 Si 5 N 8 is 2.1 while for Eu2+ doped Ce+3 2.6–2.9 • Plasmonic resonances appear at 12.5 eV and for doped – at 10.5 eV. • Main perspectives of eh further improvements of the optical constants are given. [ABSTRACT FROM AUTHOR]

Abstract Optical and magnetic features of the A 2 V 2 O 2 (A = F e and C o) compounds are explored. Density functional theory (DFT) within a framework of FPLAPW (full-potential linearized augmented plane wave) method, as well as generalized gradient approximation plus the Hubbard parameter (GGA+U) and Hubbard on-site Coulomb interaction corrections are applied. U is evaluated assuming constraint generalized gradient approximation for transition metals Fe/Co and V. The calculated band structures for the Fe doped compounds demonstrate the metallic nature while for the Co doped we observe half metallicity possessing 100% spin polarization in the vicinity of the Fermi level. The influence of Fe/Co and V magnetic moment (μ B) on the electronic, magnetic and optical features is explored in details additionally. The optical constants reveal the strong response for A 2 V 2 O 2 (A = F e and C o) in the IR (infra-red region) and UV (Ultra Violet) regions. Graphical abstract Image 1 Highlights • A 2 V 2 O 7 (A = Fe and Co) band structure was studied by functional theory based on FP-LAPW. • The spin polarized structure is more stable as that of without spin structure. • From the Fermi surface Co 2 V 2 O 7 has higher electrical conductivity as compared to Fe 2 V 2 O 7. • Spin polarized magnetic moments is 19.356 μ B (Fe 2 V 2 O 7), 14.002 μ B (Co 2 V 2 O 7). [ABSTRACT FROM AUTHOR]