Figure 4.

First $\pi$ ionization energy and first $\pi$-${\pi }^{*}$ excitation energy of pyrimidines calculated via our LCAO method using all valence orbitals, along with results at the IP-EOMCCSD/aug-cc-pVDZ (vertical ionization energies) and CR-EOMCCSD(T)/aug-cc-pVDZ (vertical excitation energies) level of theory [29], as well as available experimental data.