The one-dimensional Hubbard model at half-filling is studied in the framework
of the Composite Operator Method using a static approximation. A solution
characterized by strong antiferromagnetic correlations and a gap for any
nonzero on-site interaction U is found. The corresponding ground-state energy,
double occupancy and specific heat are in excellent agreement with those
obtained within the Bethe Ansatz. These results show that the Composite
Operator Method is an appropriate framework for the half-filled Hubbard chain
and can be applied to evaluate properties, like the correlation functions,
which cannot be obtained by means of the Bethe Ansatz, except for some limiting
cases.Comment: 7 pages, 3 embedded Postscript figures, EuroTeX, submitted to
EuroPhysics Letter
