PbTiO3 (PT) and PbZrO3 (PZ) are the two primary blocks of the solid solution PbZr1-x Ti x O3 (PZT). They can be modelled in different ways; but, in order to do comparable DFT calculations on PZT, with different values of x, one must find a unique method that can be used for both PT and PZ. In particular, we want to evaluate their vibrational properties to compare them with experimental data. Density functional theory (DFT) is used to perform structure geometry optimizations and electronic structure calculations, both on low- and high-temperature phase. Then, harmonic vibrational frequencies of their low-temperature phase are determined for transverse and longitudinal optical (TO & LO) phonons. Moreover, a detailed study of the eigenvectors shows that accurate calculations are necessary to correctly interpret and understand the IR spectra. In the end, the comparison of our theoretical results with previous experimental and theoretical data confirm the strong potential of the SOGGA (second-order generalized gradient approximation) functional to correctly describe PT, PZ and, hopefully, PZT; especially their structural and vibrational properties.