ChemRxiv
These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
1/1
0/0

On the Choice of Coordinates in Anharmonic Theoretical Vibrational Spectroscopy

preprint
revised on 28.11.2018 and posted on 29.11.2018 by Paweł T. Panek, Adrian Hoeske, Christoph R. Jacob
By a suitable choice of coordinates,the computational effort required for calculations of anharmonic vibrational spectra can be reduced significantly. By using suitable localized-mode coordinates obtained from an orthogonal transformation of the conventionally used normal-mode coordinates, anharmonic couplings between modescan be significantly reduced. However, such a transformation introduces harmonic couplings between the localized modes. To elucidate the role of these harmonic couplings, we consider vibrational self-consistent field (VSCF) / vibrational configuration interaction (VCI) calculations for both few-mode model systems and for ethene as a molecular test case. We show that large harmonic couplings can result in significant errors in localized-mode L-VSCF/L-VCI calculations and study the convergence with respect to the size of the VCI excitation space. To further elucidate the errors introduced by harmonic couplings, we discuss the connection between L-VSCF/L-VCI and vibrational exciton models. With the help of our results, we propose an algorithm for the localization of normal modes in suitable subsets that are chosen to strictly limit the errors introduced by the harmonic couplings while still leading to maximally localized modes.

Funding

Deutsche Forschungsgemeinschaft (DFG), grant JA 2329-2/1

History

Email Address of Submitting Author

c.jacob@tu-braunschweig.de

Institution

TU Braunschweig

Country

Germany

ORCID For Submitting Author

0000-0002-6227-8476

Declaration of Conflict of Interest

None

Version Notes

Included Jupyter Notebooks as Supporting Information

Exports