Fig. 4. Comparison of oxygen K-edge NEXAFS spectra at the RASPT2 and ADC level for the lowest valence singlet states (S0: black, S1: blue, S2: green) at the FC point. (a) CVS-ADC(2)-x/6-311++G**, and (b) RASPT2(18,0/1,0; 2,12,0)/cc-pVDZ. The latter have been uniformly shifted by −4.254 eV to align with the steady-state spectrum at the ADC level. The lowest vertical core-ionization energies, corresponding to a 1s(O1) hole, are indicated by dashed lines. The stick spectra were convolved with a Gaussian line shape (FWHM: 0.25 eV). (c) Dominant configurations (weight > 0.1) to the five lowest core-excited states ordered by weight from the RASPT2 calculation. Orbitals are state-averaged natural orbitals from the core-excited state calculation.
