Last, selected minimum energy and MECI structures of cytosine were determined with CASSCF and CASPT2, and relative energies were compared with MRCI calculations from Ref. 78. For comparison, the same basis set (cc-pVDZ) and active space (CAS(12e,9o) with four π, three π * , one n N , and one n O orbitals) were selected, and the first four states (SA4)