Important components for accurate hyperfine coupling constants: electron correlation, dynamic contributions, and solvation effects

ABSTRACT

The calculation of hyperfine coupling constants is a challenging task in balancing accuracy and computational effort. While previous work has shown the importance of electron correlation and molecular dynamic contributions, we present a systematic study simultaneously analyzing the influence of both effects on hyperfine coupling constants. To this end, we thoroughly study two organic radicals, namely the dimethylamino radical and ethanal radical cation, proving the need to account for conformational flexibility as well as the large influence of electron correlation. Based on these results, we analyse the effect of electron correlation and dynamic simulations on a set of 12 organic radicals, illustrating that both effects are vital for an accurate in silico description on the same scale. Furthermore, we study the influence of solvation using the efficient nuclei-selected algorithm to obtain hyperfine coupling constants with electron correlation for large systems, indicating the necessity to include explicit solvent molecules. Finally, we introduce a composite approach to incorporate all contributions for hyperfine coupling of radicals in solution at comparatively low computational cost. This is successfully tested on the hydroxylated TEMPO radical in aqueous solution, where we are able to compute a ${}^{14}$N-HFCC of 44.4 MHz compared to the experimentally measured 47.6 MHz.

GRAPHICAL ABSTRACT

KEYWORDS:

• Computational chemistry
• hyperfine coupling constants
• molecular dynamics
• electron correlation
• solvation effects

Acknowledgments

We dedicate this work to Professor Jürgen Gauß on the occasion of his 60th birthday. The authors thank Henryk Laqua (LMU Munich) for help and discussions with respect to the seminumerical calculations.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

S.V. thanks the Studienstiftung des Deutschen Volkes for a graduate fellowship. C.O. acknowledges funding by the “Deutsche Forschungsgemeinschaft” (DFG, German Research Foundation) - SFB 1309 - 325871075 and - EXC 2089/1-390776260 (excellence cluster e-conversion), as well as financial support as a Max-Planck Fellow at the Max Planck Institute for Solid State Research in Stuttgart.