title: Application of classical simulations for the computation of vibrational properties of free molecules.
abstract: In this study, we investigate the ability of classical molecular dynamics (MD) and Monte-Carlo (MC) simulations for modeling the intramolecular vibrational motion. These simulations were used to compute thermally-averaged geometrical structures and infrared vibrational intensities for a benchmark set previously studied by gas electron diffraction (GED): CS2, benzene, chloromethylthiocyanate, pyrazinamide and 9,12-I2-1,2-closo-C2B10H10. The MD sampling of NVT ensembles was performed using chains of Nose-Hoover thermostats (NH) as well as the generalized Langevin equation thermostat (GLE). The performance of the theoretical models based on the classical MD and MC simulations was compared with the experimental data and also with the alternative computational techniques: a conventional approach based on the Taylor expansion of potential energy surface, path-integral MD and MD with quantum-thermal bath (QTB) based on the generalized Langevin equation (GLE). A straightforward application of the classical simulations resulted, as expected, in poor accuracy of the calculated observables due to the complete neglect of quantum effects. However, the introduction of a posteriori quantum corrections significantly improved the situation. The application of these corrections for MD simulations of the systems with large-amplitude motions was demonstrated for chloromethylthiocyanate. The comparison of the theoretical vibrational spectra has revealed that the GLE thermostat used in this work is not applicable for this purpose. On the other hand, the NH chains yielded reasonably good results.
authors.affiliation: Universität Bielefeld, Lehrstuhl für Anorganische Chemie und Strukturchemie, Universitätsstrasse 25, 33615, Bielefeld, Germany. denis.tikhonov@uni-bielefeld.de and M. V. Lomonosov Moscow State University, Department of Physical Chemistry, GSP-1, 1-3 Leninskiye Gory, 119991 Moscow, Russia.
authors.forename: Denis S
authors.identifier: http://orcid.org/0000-0003-3167-3104
authors.initials: DS
authors.lastname: Tikhonov
authors.affiliation: Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Department Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91052 Erlangen, Germany.
authors.forename: Dmitry I
authors.initials: DI
authors.lastname: Sharapa
authors.affiliation: Universität Bielefeld, Lehrstuhl für Anorganische Chemie und Strukturchemie, Universitätsstrasse 25, 33615, Bielefeld, Germany. denis.tikhonov@uni-bielefeld.de.
authors.forename: Jan
authors.initials: J
authors.lastname: Schwabedissen
authors.affiliation: ETH Zurich, Department of Materials, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland. vladimir.rybkin@mat.ethz.ch.
authors.forename: Vladimir V
authors.identifier: http://orcid.org/0000-0001-5136-6035
authors.initials: VV
authors.lastname: Rybkin