Role of electron-electron correlation in the valence states of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7:$ Low-energy excitations and Fermi surface

We have studied the role of on-site correlation in the low-energy excitations of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ in the normal state, calculating self-energies and spectral functions according to the three-body-scattering approach. The method allows to include all the details of realistic ab initio band-structure calculations and to augment them with the inclusion of electron-electron correlations, getting quasiparticle energies for one-particle removal. It is found that correlation effects modify the energy dispersion of hole quasiparticle states, both in the high and low binding energy region, and strongly modify the Fermi surface topology.