where the sums over i includes all HF doubly occupied orbitals, and the sums over a initially includes all virtual orbitals generated in the orbital construction step. We will eventually select high-entropy orbitals for the active space, but in our previous work, we have found the entropies calculated with the full sums to be overly biased towards doubly occupied orbitals, resulting in less-than-optimal active spaces. Therefore, we use a virtual-orbital removal step in which the C ia involving the highest-entropy virtual orbital is removed from the sums in equations 7, and the entropies are recalculated. After N such virtual-orbital removal steps are taken, the entropies of the removed virtual orbitals are set to the maximum entropy of the remaining orbitals plus some small value, decreasing in order of removal; we have found good results for small-to-medium-sized organic molecules with N = 2, which is used in this work. The entropies obtained after the N removals are now used for the rest of the procedure without recalculation.