Nuclear Quantum Effects on Non-Adiabatic Molecular Dynamics

Ultrafast processes involving the interaction of matter with light are responsible for many important natural phenomena, such as vision or photosynthesis, but they are also exploited in numerous applications, e. g. for the construction of photonic materials and devices. A understanding of photo-induced processes is therefore an indispensable requisite to the practical design of photo-active functional materials. The aim of this project is to provide a general method that enables studying of photoreactions, including nuclear quantum effects and non-adiabatic dynamics in a unified approach here applied to photochromic systems. The important advantages of the proposed method are full-dimensionality, efficiency and transferability, which make it applicable to particularly difficult problems, such as excited state proton transfer, where nuclear quantum effects play an important role. The novelty of the proposed method consists in simultaneous description of the quantum mechanical nature of atomic nuclei (responsible for zero point vibrational energy, delocalization and tunneling) and non- adiabatic transitions among electronic excited states (resulting e. g. from the absorption of light). Nuclear motion will be propagated in real time using a set of appropriately coupled trajectories in full-dimensional space, while the electronic motion will be calculated on-the-fly. The advantage of this combined approach with respect to wavefunction-based nuclear quantum dynamics is that a priori knowledge of the interaction potentials is not necessary, while nuclear quantum effects are included. The capabilities of the newly developed technique will be demonstrated by studying the photo- induced proton transfer reaction in beta-thioxoketones, a prominent class of photochromic materials. Despite a rich collection of experimental data the molecular mechanism of photoreaction that these systems undergo upon photo-excitation has eluded researchers until now. This project will provide the first full-dimensional non-adiabatic dynamical simulations including nuclear quantum effects of such systems. These are expected to provide unprecedented understanding of photoreactivity in this wide family of photochromic compounds, setting up standards to investigate photo-induced proton transfer reactions, thereby paving the way to the design of functional photochromic materials.