Numerical results for generalized RVB wavefunctions

Numerical results are presented for a generalized resonance valence bond state which includes both ionic and covalent contributions in each bond ; non nearest-neighbor bonds are also considered. Variational calculations have been performed and the space group symmetry has been taken into account. The results for the Hubbard Hamiltonian are compared with the exact ones for the $2 X 2 X 2$ and the $4 X 4$ lattices. The agreement is quite satisfactory for large values of the interaction U ( for U=40 the overlap with the exact ground state wave function is 0.999 ). Several correlation functions are also compared.