The frequencies of normal modes of vibration (for a wave vector
k = 0) of cubic BaTiO
3 are calculated. It is shown that the purely ion crystal BaTiO
3 could not be stable and the covalent bonds are therefore calculated by introducing effective charges. It is found that the lowest optical frequency substantially depends on the magnitude of the Coulomb interactions and is much lower than the other optical frequencies. The results are used to interpret the infra-red spectra of BaTiO
3.