Performance of the DLPNO-CCSD and recent DFT methods in the calculation of isotropic and dipolar contributions to 14N hyperfine coupling constants of nitroxide radicals

Abstract

B3LYP, ωB97x, B2PLYP, and the B3LYP/N07D and PBE/N07D schemes in the calculation of the 14 N anisotropic hyper ne coupling (HFC) constants of a set of 23 nitroxide radicals is evaluated. The results are compared with those obtained with the DLPNO-CCSD method and experimental HFC values. Harmonic contribution to the 14 N HFC vibrational correction was calculated at the revPBE0/def2-TZVPP level and included in the evaluation. With the vibrational correction, the DLPNO-CCSD method yielded HFC values in good agreement with the experiment (MAD = 0.3 G for the dipole-dipole contribution and MAD = 0.8 G for the contact coupling contribution). The best DFT results are obtained using the M06 functional with mean absolute deviation (MAD) = 0.2 G for the dipole-dipole contribution and MAD = 0.7 G for the contact coupling contribution. In general, vibrational correction signi cantly improved most DFT functionals' performance but did not change its overall ranking.

Electron correlation and vibrational effects in predictions of paramagnetic NMR shifts

“…Excellent performance and reliability of the DLPNO-CCSD method for prediction of hyperfine and quadrupolar coupling constants was quickly recognized. 98–102…”

“…Excellent performance and reliability of the DLPNO-CCSD method for prediction of hyperfine and quadrupolar coupling constants was quickly recognized. [98][99][100][101][102] The main objectives of this study were to (i) demonstrate the applicability of the DLPNO-CCSD method for hyperfine tensor calculations within the current formalism for prediction of induced paramagnetic NMR shifts, and to (ii) incorporate vibrational corrections to isotropic orbital NMR shielding and hyperfine tensor. The inclusion of additional physics through electron correlation (i) and vibrational effects (ii) aimed at improving the accuracy and reliability of the existing protocol.…”

Reliable Isotropic Electron-Paramagnetic-Resonance Hyperfine Coupling Constants from the Frozen-Density Embedding Quasi-Diabatization Approach

“…To assess the quality of the obtained HFCCs, we calculated root-mean-square deviations (RMSDs) and mean absolute errors (MAEs) over all atoms ( 1 H, 13 C, 14 N, and 17 O) of the entire S22 set. To that end, the DLPNO–CCSD method was used as a reference, as it has been shown to provide very accurate EPR HFCCs. − The RMSDs are presented in Figure . The MAEs show qualitatively similar behavior to RMSDs and are given in Figure S2 in the SI.…”

“…Correlated ab initio wave function approaches are often used to calculate accurate EPR HFCCs − but are computationally very demanding and, thus, not feasible for large (bio)­molecular systems. Methods such as coupled-cluster singles and doubles (CCSD) employing the domain-based local pair natural orbital − (DLPNO) approximation are still computationally feasible for medium-sized radical systems and have, therefore, been used in extensive benchmarks on nitroxide radicals, − transition-metal complexes, − or small organic radicals providing very accurate results. The size limitation in HFCC computations is often lifted by using Kohn–Sham density-functional theory (KS-DFT) .…”

“…Note that we do not aim at a comparison with experimental data but will only consider single point calculations. Experimentally measured HFCCs are often strongly influenced by the dynamics (such as vibrational motion) of the studied system (see, e.g., refs , , and ). To account for those effects, vibrational corrections can, e.g., be calculated via a perturbative approach − as was done, e.g., in ref , or by carrying out conformational sampling using molecular dynamics simulations. , …”