Simulating Vibrational Spectra of Variously-sized Molecules via Multiple Coherent Time Averaging Semiclassical Initial Value Representation

The efficient and accurate calculation of molecular vibrational energies has stimulated the development of many different techniques in recent years. Among them are variational quantum approaches, semiclassical methods, ring polymer and centroid molecular dynamics. In the semiclassical field, the time averaging semiclassical initial value representation (TA-SCIVR) has represented a cornerstone for molecular spectra simulations, by providing an effective way to speed up the convergence of the multi-dimensional Monte Carlo integration. A recent advance, called multiple coherent time averaging semiclassical initial value representation (MC-TA-SCIVR) has allowed to further reduce computational overheads to just a few classical trajectories, thus permitting to extend calculations based on pre-fitted potential energy surfaces to on-the-fly ab initio simulations suitable for larger-size molecules. We present the latest developments of the MC-TA-SCIVR technique performed in our group with application to a set of molecules of different complexity.