Combined experimental and DFT approach to BiNbO₄polymorphs

Abstract

Here we present a detailed ab initio study of two experimentally synthesized bismuth niobate BiNbO4 (BNO) polymorphs within the framework of density functional theory (DFT).

An ab initio DFT perspective on experimentally synthesized CuBi2O4

“…The characteristic MB dye absorption occurs near 663 nm as expected for both pH values. 46 The intensity of the MB characteristic absorption peak is undergoing reduction over time demonstrating the destruction of the chromophoric structure of the dye. The HCBO photocatalytic degradation efficiency was derived from the linear rate equation to be 54.97% (69.86%) for a solution pH value of 5 (10) after 3 h of exposure (see Fig.…”

“…46,53,54 The simulated dielectric tensor for an unpolarized electromagnetic wavedriven back-scattered geometry, when differentiated using the nite difference method, yields the desired Raman tensor. 46,75 In the case of Raman peak position simulation, we make use of QUANTUM-ESPRESSO (QE) with the same aforementioned simulation parameters except the plane wave cut-off was set to 400 eV for LDA and 500 eV in cases of GGA-PBE and GGA-PBE+U functionals. [76][77][78][79][80][81][82]…”

“…The electronic BS calculated from GGA-PBE, GGA-PBE+U, and HSE06 were used to obtain the dipole transition matrix elements to estimate the 3 imag . 46,53,54 The 3 real is derived from 3 imag with Kramer-Kronig relation. Having both 3 real and 3 imag in hand, one can further obtain absorption coefficient a, reectivity R, energy loss function L, refractive index h, extinction coefficient K, and optical conductivity s that dene the optical behavior of the CBO in the linear regime as shown in Fig.…”

“…42 Recently, the tuning of a HF parameter has shown to produce more accurate electronic structure simulation as compared to that of the experimental values. 46,47 It is hard to nd detailed investigations of optical properties, Raman tensor, infrared response, elastic properties, and born charge tensor of CBO in combination with experimental observations in the existing literature. A DFT-guided experimental approach has proven to be invaluable for gaining a better understanding of the CBO functional properties.…”

“…The sophisticated HSE06 with Hartree-Fock exactexchange mixing parameter a HF = 25% although preserves the overall nature of orbital mixing and bandwidths of VB as CB to that of GGA-PBE+U, it increases the forbidden gap between VBM and CBm to 2.58 eV as shown in Fig.13(a). The forbidden energy gap can be tuned by changing the Hartree-Fock mixing parameter a HF 46,47. The energy gap is reduced to 1.55 eV by reducing the exact-exchange mixing a HF to 14% as displayed in Fig.13(b).…”