Dynamical screening in La2CuO4

We show that the dynamical screening of the Coulomb interaction among Cu-d electrons in high-T_c cuprates is strong and that a proper treatment of this effect is essential for a consistent description of the electronic structure. In particular, we find that ab initio calculations for undoped La₂CuO₄ in the paramagnetic phase yield an insulator only if the frequency dependence of the Coulomb interaction and the interatomic interaction between p and d electrons are taken into account. We also identify a collective excitation in the screened interaction at 9 eV, which is rather localized on the copper site, and which is responsible for a satellite structure at energy -13 eV, located below the p bands.