DFT study on ferroelectricity of BaTiO3

The ferroelectricity of BaTiO3 is investigated with the plane-wave pseudopo tential method and the LCAO quantum chemical approach in the framework of d ensity functional theory (DFT). Potential energy surfaces of various atomic displacements and the influence of lattice strain and lattice volume on th e surfaces are examined. On the basis of the potential surfaces, phonon fre quencies are also computed, which me in agreement with experiment results. The obtained potential energy surfaces show that the ferroelectric phase tr ansition (from the cubic to the tetragonal phase) is decisively controlled by Ti displacement, The larger the lattice volume and the ratio c/a, the de eper the potential well. The calculated electronic populations and static c harges show that from cubic to tetragonal phases Ti and O1 lose charges whe reas Pa and O2 gain charges. The bond orders reveal that Ba-O has some exte nt of covalency, and during the phase transition the chemical bonding betwe en metal and oxygen atoms, especially the Ti-Ol bond, is enhanced. Our resu lts seem consistent with the vibronic theory about the origin of ferroelect ricity of BaTiO3.