Accurate Calculations of a Solid State Test Set with Quantum Monte Carlo Methods

Quantum Monte Carlo (QMC) methods serve as some of the most promising techniques for studying correlated materials across large spans of system size. Here, we revisit a solid state test set for QMC ranging from ionic, metallic, covalent, and van der Waals materials.
Using the familiar fixed-node Diffusion Monte Carlo (DMC) and the more recent auxilliary field quantum Monte Carlo (AFQMC), we examine the bulk ground state properties from ambient conditions up to nearly 300 GPa. One of the key limitations to the accuracy of previous DMC calculations for this set was the quality of the effective core potentials utilized. In this work, we use the recently developed correlation consistent effective core potentials and compare to previous calculations to quantify the size of the pseudopotential errors in DMC on the calculated structural properties. Additionally, we directly compare AFQMC to DMC in order to understand the relative stengths and weaknesses of the two methods for these calculations.