Ground-state energy of strongly correlated electronic systems

Abstract

We 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-T _c 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/(ε _p −ε _d ))⁶. Heret is thep-d hopping matrix element and ε _p , ε _d are the orbital energies of the O(2p _x(y)) and$Cu(3d_{x^2 - y^2 } )$ electrons.