Next, we computed the Mg(1s) core-ionization energy of chlorophyll a, which consisted of 140 atoms, 492 correlated electrons, and 3890 basis functions with the CC-PCVTZ basis set. At the optimal embedding space(OES), it had 323 basis functions. The obtained core-ionization energy at DMET-IP-CVS-EOM-CCSD*/CC-PCVTZ was 1308.87 eV. The previously reported DLPNO-EOM-CCSD/6-311++G** result was 1311.84 eV, which was without relativistic effects. Repeating our calculations without using the perturbative triples correction and using the 6-311++G** basis set yielded 1310.92 eV. At the 6-311++G** basis set, it had 1978 basis functions, while at the CC-PCVTZ basis set, it had 3890 basis functions.