We use Quantum Monte Carlo methods to determine T = 0 Green functions, G( r, ω), on lattices up to 16 × 16 for the 2D Hubbard model at U/t = 4. is approached from the insulating phase. ξ l may be interpreted as the localization length involved in transferring a particle over a distance r from the electronic system to the heat bath lying at energy µ within the charge gap. Under the assumption of hyperscaling, the above quantities are expected to satisfy the scaling relations:where The Hubbard model we consider reads:Here, i, j denotes nearest-neighbors. c † i,σ (c i,σ ) creates (annihilates) an electron with zcomponent of spin σ on site i and n i,σ = c † i,σ c iσ . In this notation half-band filling corresponds to µ = 0. We start by considering the non-interacting case, U/t = 0. In Fourier space, the single particle energies are given by ǫ k = −2t(cos( k a x ) + cos( k a y )), a x , a y being the lattice constants. In this letter, the length scale is set by: | a x | = | a y | = 1. At zero temperature, an insulator-metal transition will occur when µ → µ c = 4t. For those chemical potentials, the zero-temperature Green function [3] at ω = µ is given by:where N denotes the number of sites of the square lattice and the factor 2 corresponds to the summation over the spin degrees of freedom. Numerically, one obtains: G( r, ω = µ) ∼ e Here, b † creates an electron in the impurity state at the origin and energy ǫ b . The hybridization between the localized state and the band electrons alters the energy of the impurity level to the value:. We will assume E b > ǫ k for all k. When all single