An application of second and third-order n-electron valence state perturbation theory to the calculation of the vertical electronic spectrum of furan

The vertical electronic spectrum of furan is investigated by second and third-order multireference perturbation theory (NEVPT). The excitation energies of the three lowest-energy valence states, as well as the 3l Rydberg states are reported. The effects of the size of the active space and the valence-Rydberg mixing are discussed. The application of the quasi-degenerate NEVPT approach has proved to be necessary in order to handle the consistent valence-Rydberg interactions occurring for the two 1A1+and1B2+ valence states. For the three valence states and the low-lying Rydberg states, the computed excitation energies agree with those computed in the more recent high-level theoretical studies.

The vertical electronic spectrum of furan is studied by second and third-order multireference perturbation theory (NEVPT). Only the three lowestenergy π → π∗ valence states and the 3s, 3p and 3d π- and π-type Rydberg states are considered. Particular attention is paid to strong valence-Rydberg mixing occurring for the two ionic valence states.