Besides this, when going to higher order polyacenes, the increasing near degeneracy of frontier orbitals (see Figure and S10 in SI), induces strong electron correlation effects. Such molecular systems with high static correlations possess inherent multi-configurational character, which is well reflected from the <S 2 > BS values (Table in SI). The mean value of S 2 operator for the unrestricted m s = 0 BS determinant should be 1.0, however < S 2 > BS values exceeding 1.0 from n =8 onward indicates the contribution from the components of higher spin multiplicities and hence reflecting the multi-configurational character. two-step procedure called DMRG-PDFT to compute the singlet-triplet gaps, however the study was rather limited to n=7 acenes. Thus, although, multi-reference methods give better insights in to the electronic structure calculations of strongly correlated molecules.