Keeping the cost down is important in many applications. Figure shows that the dependence of MC-PDFT compute times on grid size is a significant consideration; we observe a roughly 10× increase in cost from grids_level = 3 (3.4 s) to grids_level = 9 (30.8 s). Our studies find that the standard grids_level = 3 in PySCF is sufficient for excitations such as those we have calculated because we only see a significant change between the maximum and default grid size for a single excitation (SI Figure ). Therefore we recommend standard grid sizes for most applications involving state-averaged MC-PDFT.