Application of time-dependent density functional theory to electron-vibration coupling in benzene

Optical properties of symmetry-forbidden pi-pi transitions in benzene are calculated with the time-dependent density functional theory (TDDFT), using an adiabatic LDA functional. Quantities calculated are the envelopes of the Franck-Condon factors of the vibrationally promoted transitions and the associated oscillator strengths. The strengths, which span three orders of magnitude, are reproduced to better than a factor of two by the theory. Comparable agreement is found for the Franck-Condon widths. We conclude that rather detailed information can be obtained with the TDDFT and it may be worthwhile to explore other density functionals.