Construction of First Principle Based Adiabatic and Diabatic Hamiltonian for TiO68- unit of BaTiO3 Crystal: Photoemission Spectra and Ferroelectricity
Abstract
The ferroelectric property of BaTiO3 crystal arises from the strong Pseudo Jahn-Teller (PJT) interactions between the non-degenerate ground electronic state, 1A1g and the degenerate 1T1u symmetry states through the nuclear distortions of t1u modes in TiO68- unit. In a d0 electronic configuration of Ti4+ ion, the PJT interaction leads to a stabilization effect, which has been explored using Beyond Born-Oppenheimer (BBO) theory. The 1T1u excited states form a three-state degeneracy, exhibiting feeble Jahn-Teller (JT) distortions over the t2g planes. For the first time, we compute ab initio adiabatic potential energy surfaces (PESs) and non-adiabatic coupling terms (NACTs), and thereafter, diabatic PESs and couplings for the perovskite unit, TiO68-. Using a Time-Dependent Discrete Variable Representation (TDDVR) approach, the theoretical photoemission spectra exhibit good agreement with the experimental ones. Moreover, the experimental observation on order parameter associated with ferroelectric properties of BaTiO3 crystal show close resemblance with present and other theoretical predictions.