Electronic, optical, vibrational and EFG properties of tetragonal BaTiO3 under pressure: By first-principles study

The First principles study on structural, electronic, Electron Field Gradient (EFG), optical and vibrational properties of tetragonal BaTiO3 have been done in the framework of Density Functional Theory (DFT). Obtained structural properties are in agreement with others, and also the electronic study shows that the tetragonal BaTiO3 has an indirect energy gap (E-g) about 1.864 eV by GGA and 2.6 eV by GGA-mbj at equilibrium state which E-g shifts toward small values by decreasing pressure. By increasing pressure to 31.479 GPa, the EFG decrease for O atom, and increase for Ba and Ti atoms that is a sign to piezoelectric property for tetragonal BaTiO3. The optical parameters were studied under pressure, such as the real and imaginary parts of the dielectric function, Loss function, reflection index, absorption coefficient, conductivity and reflection. Moreover, by applying hydrostatic pressure, the roots of the real part of the dielectric function shift toward higher energies, and the energy loss and absorption peak intensity were reduced. Finally, lattice vibration survey indicates the stability of tetragonal BaTiO3 under pressure.