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 modes can be significantly reduced. However, such a transformation introduces harmonic couplings between the localized modes. To elucidate the role of these harmonic couplings, we consider the 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.
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7 February 2019
Research Article|
February 07 2019
On the choice of coordinates in anharmonic theoretical vibrational spectroscopy: Harmonic vs. anharmonic coupling in vibrational configuration interaction
Paweł T. Panek;
Paweł T. Panek
Technische Universität Braunschweig, Institute of Physical and Theoretical Chemistry
, Gaußstraße 17, 38106 Braunschweig, Germany
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Adrian A. Hoeske
;
Adrian A. Hoeske
Technische Universität Braunschweig, Institute of Physical and Theoretical Chemistry
, Gaußstraße 17, 38106 Braunschweig, Germany
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Christoph R. Jacob
Christoph R. Jacob
a)
Technische Universität Braunschweig, Institute of Physical and Theoretical Chemistry
, Gaußstraße 17, 38106 Braunschweig, Germany
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a)
E-mail: c.jacob@tu-braunschweig.de
J. Chem. Phys. 150, 054107 (2019)
Article history
Received:
November 29 2018
Accepted:
January 14 2019
Citation
Paweł T. Panek, Adrian A. Hoeske, Christoph R. Jacob; On the choice of coordinates in anharmonic theoretical vibrational spectroscopy: Harmonic vs. anharmonic coupling in vibrational configuration interaction. J. Chem. Phys. 7 February 2019; 150 (5): 054107. https://doi.org/10.1063/1.5083186
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