We used cubic water boxes ranging in size from 38 to 1,588,868 atoms (see Tab. I). For determining the runtime (Fig. ), a target error threshold of 10 -4 was used and multiple direct space cutoff distances were tested to find the optimal cutoff (see Sec. IV D). For demonstrating control over the accuracy (Fig. ), we used a stricter target error threshold value of 10 -8 and a constant direct space cutoff of 20 Å (cell dimension) for all systems to ensure that the accuracy would only depend on the system size.