Hartree–Fock and standard density functional theory methods applied to excited states: The case of NO2

It has been shown that energies and geometries of lowest and higher excited states of symmetric molecules can be calculated with reasonable accuracy by Hartree–Fock (HF) and standard (time-independent) density functional theory (DFT) methods. In the example of NO2, the geometries of 15 excited doublet states in C2v symmetry, (1–5)2A2, (1–5)2B1, and (1–5)2B2 were optimized by UHF and DFT (UB3PW91) with a 6-311+G(3df) basis set, all resulting from single excitations with respect to the 2A1 ground state. Energies and optimized geometries compare well with available literature values. Vertical HF and DFT excitation energies for these states have been compared with multireference configuration interaction and time-dependent DFT values. Examples of DFT optimized doubly and triply excited doublet states are given.