Deterministic quantum mechanics and heavy-atom tunneling

A classical description of nuclear motion is sufficient for the simulation of quite many reactions. In the present study, we investigate if this is also true for the isomerization reactions of diyls which were discussed as an example for heavy-atom tunneling. We find that a classical description in the frame of ab-initio molecular dynamics works well for describing these ring-closure reactions. More important than a quantum-mechanical description of nuclear motion is the explicit treatment of the environment which influences the reactions strongly. We find a significant kinetic isotope effect in the molecular dynamics simulations which was previously attributed to a quantum-mechanical nuclear motion.