A DFT+U look into experimentally synthesized monoclinic scheelite BiVO4

Abstract

We present a combined experimental and Hubbard interaction corrected density functional theory (DFT+U) based study of monoclinic scheelite (ms) bismuth vanadate BiVO4 (BVO). The ms-BVO samples were synthesized using the standard solid state reaction technique. The ms phase of the synthesized BVO samples has been confirmed from Rietveld analysis of the powder x-ray diffraction pattern and room temperature Raman spectroscopy. Both experimentally obtained crystal parameters and Raman peak positions were benchmarked against the DFT+U simulations. The variations in morphology and chemical concentrations due to different sintering temperatures and milling times were analyzed using field emission scanning electron microscopy and energy dispersive x-ray spectroscopy. The measured energy bandgap in the range of 2.38–2.58 eV from UV-Vis-NIR diffuse reflection spectroscopy was explained within the context of grain size variations in combination with bismuth and oxygen vacancies from DFT+U simulations.

A combined first principles and experimental approach to Bi2WO6

“…Moreover, HSE06 hybrid functional with the Hartree–Fock (HF) exact exchange mixing parameter α HF = 25% was used to simulate electronic and optical properties. 17,38,48–52 The α HF is tuned to 20% as PBE-HF20% functional to obtain better agreement with GGA-PBE+ U d + U p +vdW simulation and experimentally measured electronic band gap. 53–55 The PBE-HF α HF % functional use HSE screened approach similar to HSE06 with xc energy E HSE xc given in terms of short-range (SR) and long-range (LR) terms as E HSE xc = α HF E HF,SR x ( μ ) + (1 − α HF ) E PBE,SR x ( μ ) + E PBE,LR x ( μ ) + E PBE c ( μ )where the screening parameter μ in hybrid functionals was set to 0.2 Å −1 .…”

An ab initio DFT perspective on experimentally synthesized CuBi2O4

“…14 The presence of localized Cu-3d and Bi-5d orbitals in CBO dilutes Coulomb Interaction (CI) in the case of GGA-PBE. [53][54][55] The diluted CI is boosted by the Hubbard interaction parameter U = 7 eV in the GGA-PBE+U formalism. 34,42,56 The U parameter is material dependent and requires ad-hoc choice or parametric optimizations.…”

“…73,74 The optical properties were derived from the BS using Fermi's golden rule along with the standard Kramer-Kronig relations for GGA-PBE, GGA-PBE+U, and HSE06 functionals. 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.…”

“…The thermal annealing at the elevated 700 °C for the SCBO sample may have facilitated the larger grain growth. 53 The low temperature of 180 °C favors the small particle size of the HCBO sample. The EDX peak analysis conrms the chemical purity by identifying the expected Cu, Bi, and O elements in both SCBO and HCBO samples as shown in Fig.…”

“…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.…”