THE HALF-FILLED HUBBARD CHAIN IN THE COMPOSITE OPERATOR METHOD - A COMPARISON WITH BETHE-ANSATZ

The one-dimensional Hubbard model at half-filling is studied in the fr ameworks of the Composite Operator Method using a static approximation . A solution characterized by strong antiferromagnetic correlations an d a gap for ang non-zero on-site interaction U is found. The correspon ding ground-state energy, double occupancy and specific heat are in ex cellent agreement with those obtained within the Bethe Ansatz. These r esults show that the Composite Operator Method is an appropriate frame work for the half-filled Hubbard chain and can he applied to evaluate properties, like the correlation functions, which cannot be obtained b y means of the Bethe Ansatz, except for some limiting cases.