Oxygen 1s excitation and tetragonal distortion from core-hole effect in BaTiO3

The accurate description of the O 1s excitation in BaTiO3 has been elusive so far. In this Rapid Communication, the electronic structure and the high-resolution electron energy-loss near-edge structures of the O K edge in tetragonal BaTiO3 are investigated using first-principles calculations. The results demonstrate a clear correlation between the broadening of the lower energy fine structure and the anisotropic effects induced by the core-hole potential, which are directly related to the structural distortion occurring in tetragonal BaTiO3. Moreover, we show that a significant improvement of the description of higher-lying structures can be obtained when correcting the energy position of the Ba 4f states. This demonstrates that the O 1s spectrum can be a very effective probe of the distortion and changes in the local electronic structure, and be used as a sensitive tool for studying new materials and ferroelectric transitions.