O 2p-Hf 5d Band-edge Chemistry and Optical Response in Cubic BaHfO3: A First-principles Study

Abstract

In this article, four electronic-structure, density-of-states, projected-density-of-states and dielectric/optical datasets were studied to identify the microscopic O 2p−Hf 5d origin of the electronic gap in cubic BaHfO3 and evaluate the reliability of the optical post-processing outputs. Cubic BaHfO3 was examined using a Tran-Blaha modified Becke-Johnson (TB09/TB-mBJ) electronic-structure workflow and dielectric/optical post-processing. Calculations were performed with Quantum ESPRESSO PWSCF v7.5 for the five-atom Pm-3m cell at a = 7.8000 a.u. (4.1276 Å), using scalar-relativistic ONCV pseudopotentials, 50 and 500 Ry wave-function and charge-density cutoffs, a 14 × 14 × 14 Γ-centred mesh reduced to 120 irreducible k-points, 54 electrons, 100 Kohn-Sham states, and a 1.0 × 10-10 Ry SCF threshold. The TB09 band structure places the valence-band maximum on the M-R segment within 4 meV of R and the conduction-band minimum at Γ, yielding an indirect gap of 5.748 eV and a minimum direct Γ gap of 6.022 eV. The integrated DOS is fixed at 54 electrons across a state-free interval of about 5.741 eV. Since EF = 15.616 eV is pinned to the valence-band edge, finite broadened DOS at EF is an edge effect and does not indicate metallicity. Orbital-resolved PDOS identifies O 2p states at the upper valence edge and Hf 5d states at the conduction onset, with Hf-O hybridisation. The optical response is cubic and dielectric-like: at 0.680 eV, ε1 = 4.787, ε2 = 0.011, n = 2.188, k = 0.00256 and R = 0.139; ε2 reaches its principal maximum of 7.827 at 6.858 eV. These results support cubic BaHfO3 as a wide-gap O 2p-Hf 5d dielectric oxide with ultraviolet-dominated interband response, while quantitative spectral features remain subject to finite broadening and the generalised-Kohn-Sham nature of TB09.