Electron correlations in narrow energy bands: ground state energy and metal-insulator transition

摘要

The electron correlations in narrow energy bands are examined within theudframework of the Hubbard model. The single-particle Green function andudenergy spectrum are obtained in a paramagnetic state at half-filling byudmeans of a new two-pole approximation. Analytical expressions for the energy gap, polar states concentration and energy of the system are found inudthe ground state. Metal-insulator transitions in the model at the change ofudbandwidth or temperature are investigated. The results obtained are usedudfor interpretation of some experimental data in narrow-band materials.