the embedding space utilized here involved fewer than 200 orbitals. previously reported values 537.17 eV and 537.29 eV obtained using DFT. We also calculated the N(1s) core-ionization energy of azafullerene, a heterofullerene known for its significance in interstellar organic chemistry. This system has 362 correlated electrons and, at the CC-PCVTZ basis set, it had 2594 basis functions. Employing DMET-IP-CVS-EOM-CCSD at the OES, the system had only 274 basis functions, yielding a computed N(1s) core-ionization value of 408.86 eV. After incorporating triple corrections, this value became 406.86 eV, closely aligning with the experimentally reported value of 406 eV. This highlights the significance of including higher-order excitations to enhance accuracy. On the other hand, the embedding approach enabled us to reduce the orbital space by a factor of 10.