However, in the present work we have found that in larger molecules (with >350 augcc-pVTZ basis functions) the APC entropies tend to overestimate the interaction of some virtual orbitals with the doubly occupied orbitals, artificially inflating the entropies of all doubly occupied orbitals and causing the selection of highly imbalanced active spaces (SI Figure ). To overcome this issue, we propose an algorithmic extension of APC in which high-entropy virtual orbitals are removed from consideration when calculating entropies and then assigned the maximum entropy value (i.e. treated in the same way as singly occupied orbitals). The algorithm takes the following steps: