  The four-site DCA method of including intersite correlations in the dynamical
mean field theory is used to investigate the metal-insulator transition in the
Hubbard model. At half filling a gap-opening transition is found to occur as
the interaction strength is increased beyond a critical value. The gapped
behavior found in the 4-site DCA approximation is shown to be associated with
the onset of strong antiferromagnetic and singlet correlations and the
transition is found to be potential energy driven. It is thus more accurately
described as a Slater phenomenon (induced by strong short ranged order) than as
a Mott phenomenon. Doping the gapped phase leads to a non-Fermi-liquid state
with a Fermi surface only in the nodal regions and a pseudogap in the antinodal
regions at lower dopings $x \lesssim 0.15$ and to a Fermi liquid phase at
higher dopings.
