Towards reliable references for electron paramagnetic resonance parameters based on quantum chemistry: the case of verdazyl radicals

We present an efficient and accurate computational procedure to calculate properties measurable by EPR spectroscopy. We simulate a molecular dynamics (MD) trajectory by employing the quantum mechanically derived force field (QMDFF) [S. Grimme, J. Chem. Theory Comput., 2014, 10, 4497] and sample the...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2018, Vol.20 (11), p.7661-7675
Main Authors: Massolle, Anja, Dresselhaus, Thomas, Eusterwiemann, Steffen, Doerenkamp, Carsten, Eckert, Hellmut, Studer, Armido, Neugebauer, Johannes
Format: Article
Language:English
Subjects:
Computer simulation
Couplings
Density functional theory
Electron paramagnetic resonance
Electronic structure
Mathematical analysis
Molecular dynamics
Parameters
Quantum chemistry
Radicals
Spectra
Trajectories
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Summary:We present an efficient and accurate computational procedure to calculate properties measurable by EPR spectroscopy. We simulate a molecular dynamics (MD) trajectory by employing the quantum mechanically derived force field (QMDFF) [S. Grimme, J. Chem. Theory Comput., 2014, 10, 4497] and sample the trajectory at different time steps. For each snapshot EPR properties are calculated with a hybrid density functional theory (DFT) method. EPR spectra are simulated based on the averaged results. We applied the strategy to a number of previously published and novel verdazyl radicals, for which we recorded EPR spectra. The resulting simulated spectra are compatible with experiment already before employing an additional fitting step, in contrast to those from single point electronic-structure calculations. After the refinement, the experimental data are excellently reproduced, and the fitted EPR parameters do not deviate much from the calculated ones. This provides confidence in ascribing a direct physical meaning to the refined data in terms of experimental EPR parameters rather than merely considering them as mathematical fit parameters. We also find that couplings to hydrogen nuclei have a significant influence on the spectra of verdazyl radicals.
ISSN:1463-9076
1463-9084
DOI:10.1039/c7cp05657e