Density functional computations for inner-shell excitation spectroscopy

The 1s → π* inner-shell excitation spectra of seven molecules have been studied using density functional theory along with the unrestricted generalized transition state (uGTS) approach. The exchange-correlation potential is based on a combined functional of Becke's exchange (B88) and Perdew's correlation (P86). A scaling procedure based on Clementi and Raimondi's rules for atomic screening is applied to the cc-pVTZ basis set of atoms where a partial core-hole is created in the uGTS calculations. The average absolute deviation between our predicted 1s → π* excitation energies and experimental values is only 0.16 eV. Singlet-triplet splittings of C 1s → π* transitions of CO, C₂H₂, C₂H₄, and C₆H₆ also agree with experimental observations. The average absolute deviation of our predicted core-electron binding energies and term values is 0.23 and 0.29 eV, respectively.