Ground-state energy of strongly correlated electronic systems

AbstractWe calculate the ground-state energy of strongly correlated electrons by using a twodimensional (CuO2)N system as an example. It constitutes the most important structural element of the high-Tc superconducting materials. The strong correlations are treated by projection technique. For that purpose a new form of the free energy is derived, which allows for applying that method. The ground-state energy for the half-filled band case is calculated by using a Padé approximation which agrees with series expansions up to order (t/(εp−εd))6. Heret is thep-d hopping matrix element and εp, εd are the orbital energies of the O(2px(y)) and $$Cu(3d_{x^2 - y^2 } )$$ electrons.