Gaps in Densities of States of Two Hubbard-Like Models

Results are presented for the single-particle density of states of the one- and two-dimensional simplified Hubbard and Montorsi-Rasetti model. The former does not exhibit a metal-insulator transition as a function of U. With increasing temperature and for U not too large, the gap closes and spectral weight appears at the chemical potential. The Néel temperature and the temperature range for coexistence of magnetic long-range order and a gapless density of states are determined. The latter model exhibits a metal-insulator transition of the Mott type and does not show magnetic long-range order