NEAREST-NEIGHBOR CORRELATIONS IN THE HUBBARD-MODEL

The Hubbard Hamiltonian is investigated by means of a new variational trial wave function. The trial wave function includes either intrasite and nearest-neighbor correlations in an explicit form. To calculate d ensity matrices Kikuchi's pseudo-ensemble method is used. The case of a half-filled fermionic band is carefully investigated in the limit of a large number of lattice sites. The ground state energy and correlat ion functions are determined for Bethe lattices with z = 2, 4 and 6 ne arest neighbors. (C) 1998 Elsevier Science B.V.