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.