Potential energy curves for PO, calculated using DFT and MRCI methodology

The ground state, the lowest singlet and triplet cationic states, and many valence and Rydberg states, of PO are investigated using density functional theory (DFT, with the HCTH(AC) functional) and multiconfiguration interaction (MRCI) methodologies. Extensive basis sets are used, and potential energy curves are calculated. The determined spectroscopic constants are compared with data from Huber and Herzberg. The results show that DFT predicts the principal features of the spectrum up to 7 eV. The mean absolute error for T-e for the lower states is 0.23 eV with DFT, and 0.12 eV for MRCI. These are the first DFT studies for excited states of an open shell system, and they demonstrate that DFT is a useful method to help unravel experimental spectroscopic data.