Ground state of Fermi systems with strong short-range order

A new variational method is developed to calculate the ground-state energy of a fermion system with strong short-range order. As well as intrasite cor relations, the Gutzwiller trial wave function explicitly contains nearest-n eighbor correlations. The Kikuchi pseudo-ensemble method was used to calcul ate the total energy of the fermion system. The calculations were made for the paramagnetic and antiferromagnetic phases of the half-filled Hubbard mo del. It is shown that for two- and three-dimensional lattices the short-ran ge order in the paramagnetic phase strongly influences the ground-state ene rgy whereas in the antiferromagnetic phase it is insignificant. (C) 2000 MA IK "Nauka/Interperiodica".