The Hubbard model on a square lattice in the ground state is investigated. Various aspects of Mott transition at half-filling are clarified from the quantum Monte Carlo study. Critical exponents of the transition for charge and spin correlations are estimated. For the doping concentration ∂, the charge susceptibility is proportional to ∂ _1 indicating the divergence of charge mass for ∂→0, while the spin susceptibility is always finite and not singular near ∂=0. Several theoretical consequences of the above results are discussed. Incommensurate peak amplitude of spin correlation scales as (∂-∂C)_1 with ∂C<0.01 in disagreement with RPA results In (∂-∂c). The antiferromagnetic order at the half-filling also shows strong correlation character and is not sensitive to the shape of the fermi surface, while the incommensurate peak observed away from the half-filling is sensitively suppressed by the loss of partial nesting consistently with the weak coupling picture. Comparisons with experimental indications of high-Tc oxides are made.
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