Dynamical correlation-hole approach to the Hubbard model

The Hubbard I decoupling approximation [J, Hubbard, Proc. R. Sec. London Se r. A 276, 238 (1963)] is extended by introducing a k-dependent self-energy which describes a mobile correlation hole of apposite spin propagating alon g with the electron in its way around the lattice. The theory, despite its simplicity, (1) becomes exact in the strong-coupling limit; and (2) reprodu ces with great accuracy the ground-state energy, the double occupancy, the on-site correlation functions, and the effective hopping for all the values of the Hubbard Coulomb repulsion U. It also gives reasonable spectral func tions leading to (3) a single-particle Green function showing the well-know n spectral-weight transfer between the Hubbard bands as soon as the electro n density deviates from half-filling, and (4) a momentum distribution as we ll as magnetic and charge structure factors in qualitative agreement with q uantum Monte Carlo simulations, slave-boson calculations, and conserving ap proximations like fluctuation exchange and parquet. On the other hand, as i n most decoupling schemes, liftime effects and the near-Fermi-level additio nal structure characteristic of strongly correlated electron systems are mi ssing.