Systematically improvable auxiliary-field quantum Monte Carlo for strongly correlated systems

The quest for an accurate and scalable many-body method for strongly correlated systems is still ongoing despite many years of efforts. The auxiliary-field quantum Monte Carlo (AFQMC) method is an exact many-body method, but it suffers from a sign problem that limits its usefulness. The phaseless AFQMC (ph-AFQMC) has been introduced\footnote{Zhang and Krakauer, Phys. Rev. Lett. 90, 136401 (2003)} to control the sign problem. In this work we employ the unconstrained (exact) AFQMC method on massively parallel supercomputers to systematically improve ph-AFQMC results. Applications to strongly correlated systems, including transition-metal compounds, will be presented.