  A new variational method is developed to calculate the ground state energy of
Fermi systems with strong short-range correlations. A trial wave function of
Gutzwiller's type contains additional variational parameters corresponding to
configurations of pairs of nearest-neighbor sites. To evaluate the ground state
energy, generalized Kikuchi's pseudo-ensemble method is used. The Hubbard model
at half band-filling is investigated. The ground state energy of the
paramagnetic phase is calculated for a chain, square and simple cubic lattices.
It is shown that the short-range order lowers drastically the ground state
energy of the Hubbard model at intermediate interaction strength. The
paramagnetic phase of the Kondo-Hubbard model ($S=1/2$ and $S=5/2$) at half
band-filling is investigated. The ground state energy, correlation functions
and effective mass are calculated for chain, square and simple cubic lattices.
A quantum phase transition was found for simple cubic lattice.
