Normal and Antiferromagnetic States of an Extended Hubbard Model.

Extensions of the Gutzwiller variational method are used to study the phase diagram of an extended Hubbard model on a copper- oxygen lattice in two dimensions. Antiferromagnetism appears to occur at half filling only when the oxygen p levels and copper d levels have substantially different energies. It is also found that strong nearest neighbor repulsions can enhance the tendency for local moment antiferromagnetism. The dependence of the variational parameters on the Hamiltonian parameters, particularly nearest neighbor repulsions, is examined. The implications for models of high temperature superconductivity are discussed.