Abstract
On the basis of the generalized spin-wave theory, which treats the collective transverse spin fluctuations as the main perturbation to the ground state of the mean-field theory, we calculate the ground-state energy, the spin-wave velocity, and the sublattice magnetization of the square-lattice Hubbard model at half filling. In the very-strong-coupling limit, all the results are shown to be in agreement with the ordinary spin-wave theory.