A case study of density functional theory and domain-based local pair natural orbital coupled cluster for vibrational effects on EPR hyperfine coupling constants: vibrational perturbation theory versus ab initio molecular dynamics

Abstract

Local approximations of high-level ab initio methods make superior accuracy in the computation of molecular properties accessible by drastically decreasing computational times. As a consequence, these methods become applicable not only for large systems but also in schemes for which large numbers of calculations are necessary. In this work, we apply a recently developed open-shell implementation of the domain-based pair natural orbital coupled cluster singles doubles (DLPNO-CCSD) approach for the computation of vibrational corrections to the isotropic values of electron paramagnetic resonance (EPR) hyperfine coupling constants. We assess density functional theory (DFT) and DLPNO-CCSD approaches using two common but very different schemes: (1) vibrational perturbation theory based on equilibrium geometries, and (2) explicit canonical ensemble averages using configuration snapshots sampled from revPBE0-D3(0) ab initio molecular dynamics simulations. Both approaches are found to yield very similar results for the spin probe 2,2,3,4,5,5-hexamethylperhydroimidazol-1-oxyl (HMI) and are both feasible for systems of around 30 atoms. However, the numerical stability required for higher derivatives can become a limitation for local correlation methods in the case of vibrational perturbation theory.

GRAPHICAL ABSTRACT

Keywords:

• Electron paramagnetic resonance
• hyperfine coupling constants
• ab initio calculations
• vibrational corrections
• ab initio molecular dynamics

Acknowledgments

AAA would like to acknowledge Jürgen Gauss as mentor, supporter, and friend. FN thanks Jürgen Gauss for many years of support, friendship, and guidance. With his rigorous, careful, and unbiased approach to science, he has always been a role model and his work stands out as a great inspiration for thoroughness and the spirit of right-for-the-right-reason. We would like to acknowledge the Max-Planck Society and the IMPRS ‘Recharge’ for financial support. We would also like to acknowledge Marcus Kettner for initial work on the ORCA VPT2 module which has been extended to the computation of vibrational averages in this work. Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy –EXC 2033 – 390677874 – RESOLV.

Disclosure statement

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

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy [grant number EXC 2033 – 390677874 – RESOLV] the Max Planck Society and the International Max Planck Research School on Reactive Structure Analysis for Chemical Reactions (IMPRS-RECHARGE).