Semiclassical Dynamics: A Viable Route to Molecular Spectroscopy

Reliable molecular spectroscopy simulations require an accurate quantum description of nuclear motion. Since purely quantum mechanical approaches are not affordable when dealing with high dimensional systems, an alternative path must be followed. Semiclassical methods have been demonstrated to provide a viable route to obtain quantum features starting from classical trajectories. Based on the time-averaged version of Miller’s semiclassical initial value representation, we have developed new semiclassical techniques able to yield accurate vibrational spectra upon classical evolution of just a handful of trajectories. Our techniques can be interfaced to ab initio on-the-fly dynamics and can tackle problems involving hundreds of degrees of freedom by means of a divide-and-conquer strategy. We present some relevant applications that cover a large dimensionality range, going from ammonia (with tunneling splitting detection), to glycine (with a potential energy surface characterized by multiple shallow wells) and C 60 fullerene (a system made of 174 degrees of freedom).