Validation of hybrid WC1LYP functional for ferroelectric LiNbO3 and LiTaO3 using Compton spectroscopy and first-principles computations

Abstract

Electronic structure and theoretical momentum densities (EMDs) of LiNbO3 and LiTaO3 using linear combination of atomic orbitals (LCAO) scheme are deduced. Present energy bands and density of states using local density approximation, generalised gradient approximation and hybrid (HF + DFT) PBE0 and WC1LYP schemes show a direct band gap (varying between 3.13- 5.13 eV and 3.11–5.18 eV for LiNbO3 and LiTaO3, respectively) at Γ point of Brillouin zones. The WC1LYP hybrid functional based EMDs depict reasonable agreement with present experimental Compton lines (using 100 mCi Am-241 γ-ray Compton spectrometer) than other investigated exchange-correlation potentials, thereby suggesting the applicability of hybrid model like WC1LYP in such ferroelectrics. Accuracy of energy bands is also ensured via electronic and optical properties using modified Becke–Johnson potential as facilitated in the full-potential linearized augmented plane wave method. Presently reported UV–vis measurements for optical band gaps are in consonance with the hybrid potential (WC1LYP) for the both ferroelectrics, which further confirms usefulness of hybrid scheme. Moreover, equal–valence–electron–density scaled experimental data reveal more covalent character of LiNbO3 than that in LiTaO3, which is in agreement with the present LCAO based Mulliken's population analysis.