Constrained path quantum Monte Carlo method for fermion ground states.

We propose a new quantum Monte Carlo algorithm to compute fermion ground-state properties. The ground state is projected from an initial wave function by a branching random walk in an over-complete basis space of Slater determinants. By constraining the determinants according to a trial wave function {vert_bar}{Psi}{sub {ital T}}{r_angle}, we remove the exponential decay of signal-to-noise ratio characteristic of the sign problem. The method is variational and is exact if {vert_bar}{Psi}{sub {ital T}}{r_angle} is exact. We report results on the two-dimensional Hubbard model up to size 16{times}16, for various electron fillings and interaction strengths.