THE LARGE-U HUBBARD-MODEL FOR A SEMIINFINITE CRYSTAL - A MOMENT APPROACH AND AN ENERGY-DEPENDENT RECURSION METHOD

Electron-correlation effects at metal surfaces can be studied qualitat ively within the framework of the Hubbard model for a semi-infinite la ttice. We propose a moment approach for an approximate determination o f the local electronic self-energy that is applicable for systems with reduced translational symmetry. For the strong-correlation regime a o ne-pole ansatz for the self-energy can be motivated. All a priori unkn own parameters in the ansatz for the self-energy are calculated self-c onsistently by exploiting the equality between two alternative but exa ct representations for the first four moments of the spectral density. With the resulting expression for the self-energy at hand, the many-b ody problem reduces to the problem of finding the local density of sta tes (LDOS) for an energy-dependent effective one-particle Hamiltonian. We determine the LDOS for the semi-infinite system using a straightfo rward generalization of the standard tight-binding recursion method th at is suitable for treating an energy-dependent Hamiltonian. The resul ting energy dependence of the recursion coefficients is studied in det ail for the (100) surface of a bcc crystal and an interpolation proced ure for a numerically feasible evaluation of the theory is suggested.