  On the example of TiO$_4$ layer (such as realized in Sr$_2$TiO$_4$) we study
electronic structure of multi-band $d-p$ models describing transition metal
perovskites. In agreement with the experiment, the studied system is predicted
to be a robust nonmagnetic insulator. A realistic treatment of electronic
structure requires one to introduce non-zero Coulomb local interactions at $2p$
oxygen orbitals. However, up till now majority of papers based upon multi-band
models made an approximation of neglecting such interactions. We show that this
simplification does not lead to serious problems in predictions of the
electronic structure provided the Coulomb interactions at titanium ions and
charge transfer gap are suitably renormalized (so they become entirely
different with respect to the true microscopic $d-p$ model parameters).
