Green's-function Monte Carlo for lattice fermions: Application to the t-J model

We develop a general numerical method to study the zero-temperature propert ies of strongly correlated electron models on large lattices. The technique , which resembles Green's-function Monte Carlo, projects the ground-state c omponent from a trial wave function with no approximations. We use this met hod to determine the phase diagram of the two-dimensional t-J model, using the Maxwell construction to investigate electronic phase separation. The sh ell effects of fermions on finite-sized periodic lattices are minimized by keeping the number of electrons fixed at a closed-shell configuration and v arying the size of the lattice. Results obtained for various electron numbe rs corresponding to different closed shells indicate that the finite-size e ffects in our calculation are small. For any value of interaction strength, we find that there is always a value of the electron density above which t he system can lower its energy by forming a two-component phase separated s tate. Our results are compared with other calculations on the t-J model. We find that the most accurate results are consistent with phase separation a t all interaction strengths.