Comparison of the magnetic properties of the Hubbard Hamiltonian in the weak correlation limmit to the HFA

Resonance broadening is included along with spin‐disorder scattering to study the magnetic properties of the Hubbard Hamiltonian in the weak correlation limit. The calculated susceptibility is compared to the exchange enhanced Hartree–Fock approximation (HFA) susceptibility, and limits are set on the applicability of the HFA. For a semicircular density of states, HFA appears to be applicable for I/Δ<0.5 and a half‐filled band, but for low electron (or hole) densities the range of applicability in I/Δ decreases.