Anharmonic calculations of vibrational spectra for molecular adsorbates : A divide-and-conquer semiclassical molecular dynamics approach

A theoretical investigation of vibrational properties of molecular adsorbates can help in understanding a large variety of phenomena, including surface catalysis. In the present work we aim in overcoming the harmonic approximation by accounting not only anarmonicities, but also quantum nuclear effects, such as overtones and combination bands. We achieve this objective by extending to the adsorption problem the divide-and-conquer semiclassical molecular dynamics approach [1], which already revealed successfully in describing vibrational levels in molecular systems. Relying on a standard Born-Oppenheimer classical trajectory of the full dimensional surface adsorbate system, we propagate at the semiclassical level only the adsorbate modes and few coupled surface ones. In this way, while containing the computational effort, we are able to obtain spectra which accounts for the effects coming from the molecular-surface interaction. We test our approach on CO, NO and H2O adsorbed on TiO2 Anatase(101), comparing our semiclassical results against the harmonic estimate and the classical power spectra computed on top on the same trajectory used for the semiclassical simulations [2]. [1] M. Ceotto, et al.,Phys. Rev. Lett. 119, 010401 (2017) [2] M. Cazzaniga, et al., J. Chem. Phys. 152, 104104 (2020)