Ergodicity at large couplings with the determinant Monte Carlo algorithm

It is known that ergodicity problems are encountered in simulating the Hubbard model at large ratios of the Coulomb interaction strength U to the hopping matrix element t using the ‘‘determinant Monte Carlo’’ algorithm with single-spin-flip moves. We discuss the potential barriers that cause this difficulty in sampling, and introduce global moves of a line of Hubbard-Stratonovich variables on a single site and all time slices to equilibrate the system. We show that at half filling these moves allow the system to explore fully the singly occupied subspace without having to move out of it, in contrast to the single-spin-flip moves of the Hubbard-Stratonovich variables where the system must pass through configurations with appreciable weight for doubly occupied or empty sites in order to go from one state in the singly occupied sector to another. We use these global moves to obtain the antiferromagnetic structure factor at large U/t.