  Current theoretical studies of electronic correlations in transition metal
oxides typically only account for the local repulsion between d-electrons even
if oxygen ligand p-states are an explicit part of the effective Hamiltonian.
Interatomic interactions such as Upd between d- and (ligand) p-electrons, as
well as the local interaction between p-electrons, are neglected. Often, the
relative d-p orbital splitting has to be adjusted "ad hoc" on the basis of the
experimental evidence. By applying the merger of local density approximation
and dynamical mean field theory (LDA+DMFT) to the prototypical case of the
3-band Emery dp model for the cuprates, we demonstrate that, without any "ad
hoc" adjustment of the orbital splitting, the charge transfer insulating state
is stabilized by the interatomic interaction Upd. Our study hence shows how to
improve realistic material calculations that explicitly include the p-orbitals.
