Each external determinant produced in the batch I pq is characterized by two indices r and s with Ôa † r a † s a p a q |I = |I rs pq . e contribution associated with each determinant of a given batch will be computed incrementally in a two-dimensional array A(r, s) as follows. A rst loop is performed over all the determinants |J belonging to the ltered internal space J I pq . Comparing |J to I pq allows to quickly identify if |J will be present in the list of external determinants, and consequently tag the corresponding cell A(r, s) as banned. Banned cells will not be considered for the computation of e α of the batch can be obtained using A(r, s). e running value of E is then incremented, I pq a er ltering out disconnected determinants of the ground state of the CN3 molecule with 935 522 determinants (see Sec. A). is example shows that, starting from Ψ (0) , the coarse-grained process which consists of removing the determinants more than quadruply excited with respect to the generator |I produces wave functions Ψ (0) I with a typical size of 120 000 determinants, a reduction by a factor 8.