Low-temperature phase of BaTiO3: Piezoelectric, dielectric, elastic, and photoelastic properties from ab initio simulations

A complete theoretical characterization of dielectric, elastic, photoelastic, and piezoelectric tensors of the low-temperature rhombohedral phase of BaTiO3 was performed by accurate ab initio simulations within periodic boundary conditions, using one-electron Hamiltonians and atom-centered Gaussian-type-function basis sets as in the CRYSTAL program. Because this phase is stable only at very low temperature, experimental characterization is difficult, and none of such tensorial properties have been measured. For this reason, we validated our method by comparing structural, electronic, and vibrational properties of the other three phases of BaTiO3 ( cubic, tetragonal, and orthorhombic) with available experimental data. The effect of the adopted one-electron Hamiltonian on the considered tensorial properties, beyond the simple local density approximation and the dependence on the electric field frequency of dielectric and photoelastic constants, is explicitly investigated.