Time-Dependent Density Functional Theory Calculations of Photoabsorption Spectra in the Vacuum Ultraviolet Region

The results of time-dependent density functional theory (TD-DFT) calculations of the transition energies and oscillator strengths of the excited states of formaldehyde, benzene, ethylene, and methane are reported. The local DFT (LDFT) transition energies tend to be smaller than experimental values by 0.1−1.3 eV. Inclusion of nonlocal (NLDFT) (gradient corrected) effects made the calculated energies larger than the LDFT values and thus made the energies closer to the experimental values for formaldehyde, ethylene, and methane. For benzene, no significant change in the calculated transition energies due to the addition of nonlocal effects was observed. The TD-DFT oscillator strengths are much better than those found at the configuration interaction singles (CIS) level. The agreement between the calculated TD-DFT values and the experimental values for the oscillator strengths is quite good, at least semiquantitative at both the LDFT and NLDFT levels.