Quantum-chemical calculation of two-dimensional infrared spectra using localized-mode VSCF/VCI


Computational protocols for the simulation of two-dimensional infrared (2D IR) spectroscopy usually rely on vibrational exciton models, which require an empirical parametrization. Here, we present an efficient quantum-chemical protocol for predicting static 2D IR spectra that does not require any empirical parameters. For the calculation of anharmonic vibrational energy levels and transition dipole moments, we employ the localized-mode vibrational self-consistent field (L-VSCF) / vibrational configuration interaction (L-VCI) approach previous established for (linear) anharmonic theoretical vibrational spectroscopy [Panek and Jacob, ChemPhysChem 15, 3365–3377 (2014)]. We demonstrate that with an efficient expansion of the potential energy surface using anharmonic one-mode potentials and harmonic two-mode potentials, 2D IR spectra of metal carbonyl complexes and of dipeptides can be predicted reliably. We further show how the close connection between L-VCI and vibrational exciton models can be exploited to extract the parameters of such models from those calculations. This provides a novel route to the fully quantum-chemical parametrization of vibrational exciton model for predicting 2D IR spectra.


Supplementary material

Supporting Information
Additional tables and figures.

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Zenodo Data Set
Data set containing: - xyz files of all considered molecular structures. - Results data from the harmonic and anharmonic vibrational calculations. - Data and code for calculating 2D-IR spectra.