Semiclassical vibrational spectroscopy from small molecules to solvated biomolecules

The hallmark of semiclassical dynamics is the ability to get quantum effects starting from classical trajectories.[1] Therefore, the main challenge semiclassical methods have to face is to demonstrate their accuracy and possibility to be applied even to large and complex systems.[2] I will show that semiclassical dynamics can be straightforwardly interfaced to different descriptions of the potential energy surface (PES), ranging from ab initio PESs[3-5] to force fields[6,7] and QM/MM schemes. This allows one to apply semiclassical spectroscopy to the calculation of the quantum vibrational features of very different systems, including not only small molecules characterized by elusive Fermi resonances, like ethanol, or hard-to-assign experimental spectra, like proline, but also large systems like solvated biomolecules. Finally, ongoing efforts to reproduce also the intensity of absorption in the framework of semiclassical dynamics will be illustrated.[8] [1] W. H. Miller The semiclassical initial value representation: A potentially practical way for adding quantum effects to classical molecular dynamics J. Phys. Chem. A 105, 2942 (2001). [2] M. Ceotto, G. Di Liberto, R. Conte Semiclassical “divide-and-conquer” method for spectroscopic calculations of high dimensional molecular systems Phys. Rev. Lett. 119, 010401 (2017). [3] R. Conte, A. Nandi, C. Qu, Q. Yu, P. L. Houston, and J. M. Bowman Semiclassical and VSCF/VCI calculations of the vibrational energies of trans- and gauche-ethanol using a CCSD(T) potential energy surface J. Phys. Chem. A 126, 7709 (2022). [4] A. Rognoni, R. Conte, M. Ceotto Caldeira-Leggett model vs ab initio potential: A vibrational spectroscopy test of water solvation J. Chem. Phys. 154, 094106 (2021). [5] G. Botti, C. Aieta, R. Conte The complex vibrational spectrum of proline explained through the adiabatically switched semiclassical initial value representation J. Chem. Phys. 156, 164303 (2022). [6] F. Gabas, R. Conte, M. Ceotto Quantum vibrational spectroscopy of explicitly solvated thymidine in semiclassical approximation J. Phys. Chem. Lett. 13, 1350 (2022). [7] D. Moscato, F. Gabas, R. Conte, M. Ceotto Vibrational spectroscopy simulation of solvation effects on a G-quadruplex J. Biomol. Struct. Dyn. doi:10.1080/07391102.2023.2180435 (2023). [8] C. Lanzi, C. Aieta, M. Ceotto, R. Conte A semiclassical approach to IR spectroscopy, being prepared.