To ensure comparability to previous results, the analysis is performed consistently for a variation of -0.5 per amino acid. For a system containing 214 amino acids (as for COMT considered below) treated according to the saaPCVA scheme (Fig. ) with a one-sided variation of -0.5 for the reactant only, 214 single point calculations with a minimal QM region are needed. These can be achieved on a short time scale compared to QM/MM geometry calculations with larger QM regions. Further information on timings can be found in Tab. S5 of Ref. .