  We present lattice results for the ground state energy of a spin-1/2 fermion
system in the unitary limit, where the effective range of the interaction is
zero and the scattering length is infinite. We compute the ground state energy
for a system of 6, 10, 14, 18, and 22 particles, with equal numbers of up and
down spins in a periodic cube. We estimate that in the limit of large number of
particles, the ground state energy is 0.25(3) times the ground state energy of
the free Fermi system.
