Importantly, HF-3c performs just as well as HF/6-31G as a supersystem correction despite using only a minimal basis set ("MINIX" ). For the 632-atom COMT enzyme-substrate complex, this means 1,944 basis functions for HF-3c/MINIX versus 3,510 functions for HF/ 6-31G. On a single 28-core node, these supersystem calculations can be completed in 0.6 h (HF-3c/MINIX) and 1.0 h (HF/6-31G), with 80-90% of that time spent in the PCM solver, which is less well-parallelized than the twoelectron integrals. (The PCM cost could be reduced by using a less dense surface discretization.)