  We show how vibronic spectra in molecular systems can be simulated in an
efficient and accurate way using first principles approaches without relying on
the explicit use of multiple Born-Oppenheimer potential energy surfaces. We
demonstrate and analyse the performance of mean field and beyond mean field
dynamics techniques for the \ch{H_2} molecule in one-dimension, in the later
case capturing the vibronic structure quite accurately, including quantum
Franck-Condon effects. In a practical application of this methodology we
simulate the absorption spectrum of benzene in full dimensionality using
time-dependent density functional theory at the multi-trajectory mean-field
level, finding good qualitative agreement with experiment. These results show
promise for future applications of this methodology in capturing phenomena
associated with vibronic coupling in more complex molecular, and potentially
condensed phase systems.
