title: Fermi resonance in CO2: Mode assignment and quantum nuclear effects from first principles molecular dynamics.
abstract: Vibrational spectroscopy is a fundamental tool to investigate local atomic arrangements and the effect of the environment, provided that the spectral features can be correctly assigned. This can be challenging in experiments and simulations when double peaks are present because they can have different origins. Fermi dyads are a common class of such doublets, stemming from the resonance of the fundamental excitation of a mode with the overtone of another. We present a new, efficient approach to unambiguously characterize Fermi resonances in density functional theory (DFT) based simulations of condensed phase systems. With it, the spectral features can be assigned and the two resonating modes identified. We also show how data from DFT simulations employing classical nuclear dynamics can be post-processed and combined with a perturbative quantum treatment at a finite temperature to include analytically thermal quantum nuclear effects. The inclusion of these effects is crucial to correct some of the qualitative failures of the Newtonian dynamics simulations at a low temperature such as, in particular, the behavior of the frequency splitting of the Fermi dyad. We show, by comparing with experimental data for the paradigmatic case of supercritical CO2, that these thermal quantum effects can be substantial even at ambient conditions and that our scheme provides an accurate and computationally convenient approach to account for them.
authors.affiliation: Département de Chimie, CNRS, PASTEUR, Ecole Normale Supérieure, PSL Research University, UPMC Univ Paris 06, 24 Rue Lhomond, 75005 Paris, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Basire
authors.affiliation: Département de Chimie, CNRS, PASTEUR, Ecole Normale Supérieure, PSL Research University, UPMC Univ Paris 06, 24 Rue Lhomond, 75005 Paris, France.
authors.forename: Félix
authors.identifier: 0000000184407753
authors.initials: F
authors.lastname: Mouhat
authors.affiliation: Département de Chimie, CNRS, PASTEUR, Ecole Normale Supérieure, PSL Research University, UPMC Univ Paris 06, 24 Rue Lhomond, 75005 Paris, France.
authors.forename: Guillaume
authors.identifier: 0000000348246512
authors.initials: G
authors.lastname: Fraux
authors.affiliation: CNRS, Institut Néel, University of Grenoble Alpes, F-38042 Grenoble, France.
authors.forename: Amélie
authors.initials: A
authors.lastname: Bordage
authors.affiliation: CNRS, Institut Néel, University of Grenoble Alpes, F-38042 Grenoble, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Hazemann
authors.affiliation: CNRS, Institut Néel, University of Grenoble Alpes, F-38042 Grenoble, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Louvel
authors.affiliation: CNRS Laboratoire Analyse et Modélisation pour la Biologie et l'Environement, UMR 8587, Unversité d' Evry-Val-d'Essonne, Blvd. F. Mitterrand, 91025 Evry Cedex, France.
authors.forename: Riccardo
authors.identifier: 000000015160489X
authors.initials: R
authors.lastname: Spezia
authors.affiliation: CECAM Centre Européen de Calcul Atomique et Moléculaire, École Polytechnique Fédérale de Lausanne, Batochime, Avenue Forel 2, 1015 Lausanne, Switzerland.
authors.forename: Sara
authors.identifier: 0000000341312513
authors.initials: S
authors.lastname: Bonella
authors.affiliation: Département de Chimie, CNRS, PASTEUR, Ecole Normale Supérieure, PSL Research University, UPMC Univ Paris 06, 24 Rue Lhomond, 75005 Paris, France.
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Vuilleumier