and excitation levels n exc between 0 and 2 were considered. Interestingly, convergence with respect to n exc is reached for 2 interspace excitations, and GAS schemes with larger n exc values were not necessary. For n exc = 1, the number of supergroups is 19 and a memory of 56.2 MB has been allocated to store the PCHB probability distributions. For n exc = 2 the number of supergroups is 85 and 250 MB are required. GAS calculations were performed in both spin pure and SD bases and compared to each other. The supporting information contains further computational details.