Ab initio molecular dynamics simulation of the UV absorption spectrum of β-ionone

Ab initio molecular dynamics have been performed at the ONIOM (B3LYP/3-21G(d):AM1) level of calculation in order to study the link between the exploration of interconversion pathways of the β-ionone compound and its UV absorption spectrum. Absorption spectra were obtained by TDDFT (B3LYP/6-31+G*) calculations which account for bulk solvent effects performed on geometries picked on different molecular dynamic trajectories. We show that, beyond the usual theoretical interpretation of UV spectra in terms of vertical excitation energies and associated oscillator strengths obtained on a single geometry, the coupling of various strategies (i.e. ab initio molecular dynamics, hybrid QM/MM methods, solvent described with polarizable continuum models and TDDFT) is now easily feasible on large molecules and provides theoretical absorption spectra which take into account dynamical effects. In that context, our code based on ab initio molecular dynamics using Gaussian-type orbitals, is able to integrate several theoretical methods.