VARIATIONAL APPROACH TO SPIN FLUCTUATIONS IN THE HUBBARD-MODEL

We study a one parameter variational wave function to improve the spin density wave ground state of the Hubbard model by inclusion of quantu m spin fluctuations. Using a perturbative approach and novel lattice s ummation techniques we present analytical as well as numerical results for the correlation energies and the staggered magnetizations in one and two dimensions. We find ground state energies which are satisfying ly close to known exact results and are significantly lower than those of existing Gutzwiller and numerical treatments.