d-wave state with multiplicative correlation factors for the Hubbard model

A d-wave state wave function with multiplicative correlation factors for th e Hubbard model is investigated using a variational Monte Carlo method. Emp loying a simple Gutzwiller-BCS wave function as a starting wave function, w e consider improved wave functions with elf-diagonal correlation factors. T he Monte Carlo simulations are carried out on a square lattice with size 10 x 10 for U = 8 and next nearest neighbor transfer t' = -0.09, The ground-s tate energy is evaluated from an extrapolation. Our wave functions show tha t pair col relation functions are enhanced for a negative value of t'.