Semiclassical Molecular Dynamics for Spectroscopic Calculations

Semiclassical molecular dynamics has long been known to be able to calculate accurately vibrational power spectra of small, isolated molecules with inclusion of quantum effects like zero-point energies, overtones, tunneling splittings, and quantum resonances. Our group introduced some methodological advances that have permitted the application of semiclassical spectroscopy to larger molecular systems up to several dozens of atoms, simulation of IR spectra, and determination of vibrational eigenfunctions. In this talk I will briefly introduce the divide-and-conquer semiclassical initial value (DC SCIVR) method and few relevant applications. Specifically, I will show how we implemented DC SCIVR with a machine learning algorithm and applied it to NMA spectra calculations using a pre-computed potential energy surface (PES). Then, a study using a water cluster PES and aimed at determining the minimum number of water molecules needed to solvate a central one, will point out the possibility for semiclassical dynamics to deal with the solvation issue. Another study of molecular adsorption on TiO2(101) Anatase surface using direct ab initio molecular dynamics will show how DC SCIVR can be employed for reproducing spectra of adsorbed molecules. Then, simulations of some relevant spectral features of nucleobases, nucleosides and an on-going study of solvated thymidine will be used to compare results based on precise ab initio on-the-fly semiclassical dynamics with those relying on force fields, providing for the latter a quantum based assessment of their accuracy. To conclude, I will show how semiclassical dynamics can provide IR spectra and nuclear marginal densities with application to glycine from ab initio direct dynamics calculations.