To illustrate the extrapolation procedure described in Sec. II D, we consider a cyanine dye 123 H 2 N -CH --NH 2 + (labeled as CN3 in the remaining) in both its ground state and rst excited state. e geometry is the equilibrium geometry of the ground state optimized at the PBE0/cc-pVQZ level. 125 e ground state is a closed shell, well described by a single reference, while the excited state is singly excited and requires, at least, two determinants to be properly modeled.