In the special case of localized MO bases, and under the assumption that I and A are from spatially distant orbitals, we have |h IA | ≈ |g IARR | ≈ |g IRRA | ≈ 0, i.e., the single excitations become vanishingly small regardless of the determinant. In light of this property, we suggest the approximation of contracting over all orbitals (R) for the weight