To show the efficiency of the present implementation, we have performed the core IP calculation on AATT nucleobase tetramer using our SS-FNO-IP-EOM-CCSD* implementation. This AATT geometry is taken from the work of Krylov and co-workers . The same molecule was used to benchmark the accuracy of the SS-FNO based implementation of IP-ADC(3). The uncontracted 6-31++g** method has been used for the calculation, which leads to 298 correlated electrons, 1218 virtual orbitals and 6062 natural auxiliary functions. The R3CVS approximation has been used for the calculation. The use of SS-FNO approximation leads to an active virtual space size of 726 and 876 natural auxiliary basis functions. Figure presents the IP-ADC (2) Dyson orbital calculated using zeroth order intermediate state representation. One can see that the core hole is localized on one of the carbonyl oxygen atoms of one thymine molecule, which is considerably different from that observed for valence ionization of AATT, where the hole was delocalized over both the adenine .