Density functional theory and ab initio studies on hyperfine coupling constants of phosphinyl radicals

Abstract

The 31P hyperfine coupling constants for various phosphinyl radicals were calculated using density functional theory (DFT) as well as the ab initio orbital‐optimized spin‐component‐scaled MP2 (OO‐SCS‐MP2) and coupled cluster methods (with relaxed and unrelaxed density). However before that, electron correlation in phosphinyl radicals was investigated by means of the fractional occupation number weighted electron density (FOD). The isotropic hyperfine coupling constants for phosphinyl radicals posed a considerable challenge to DFT; among other issues, the well‐known functional B3LYP substantially underperformed, but TPSS0 provided highly accurate results. Two tested double hybrid functionals, namely B2PLYP and mPW2PLYP, and OO‐SCS‐MP2 were found to be reasonably accurate. The unbalanced description of spin polarization in the valance region was identified as the root of the problems of DFT methods with correct prediction of the isotropic hyperfine coupling constants. In calculations at the coupled cluster level, relaxed and unrelaxed density matrices were tested and both were proved to provide highly satisfactory results for phosphinyl radicals. This was confirmed for a set of small paramagnetic species.

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

“…For example, the strongly constrained and appropriately normed semilocal density functional (SCAN) yields at the cost of a non-hybrid mGGA functional [2] electron densities better than the B3LYP functional. While the B3LYP functional is well tested [5,7,[9][10][11][12][13][14], the SCAN functional performance data are insu cient. It has been shown [5,15] that SCAN, while being competitive to the commonly used functionals in some cases, is not, in general, the best choice for HFC calculation.…”

“…The B2GP-PLYP functional was chosen for geometry optimization according to a recent benchmark study [22]. 14 N HFCC were calculated using some newer density functionals available in Libxc [23]. DFT functionals used are: strongly constrained and appropriately normed semilocal density functional (SCAN) [24] (we didn't nd signi cant differences between the results of SCAN and revised SCAN functional [25] hence the results of the calculations using the latter are not presented), hybrid SCAN0 [26] (also similar to the results of the revised version), bayesian error estimation functional (BEEF) [27], power series extension of the PBE exchange functional [28] (PBEpow exchange functional combined with the PBE [29] correlation functional), PBE-GX functional [30] (combined with the PBE correlation functional), MN15 and MN15-L functionals [31,32], PBE1KCIS hybrid [33] (with KCIS correlation functional [34]), screened Coulomb potential hybrid functional (HSE06) [35] and B98 hybrid [36].…”

“…The COSMO solvation model [21] with toluene as a solvent was used as non-polar solvents implicit solvation models were shown to yield reasonable solvent shifts [16,59]. 14 N hyper ne couplings of nitroxide radicals were also calculated using the domain-based local pair-natural orbital coupled-cluster with singles and doubles (DLPNO-CCSD) method [17,60,61] with DLPNO-HFC1 set of the thresholds and quasi-restricted orbitals (QRO) from unrestricted B3LYP/COSMO calculation as a reference. COSMO could not be used in DLPNO-CCSD calculation directly.…”

“…Only harmonic corrections, given by: see formula in the supplementary les. 14 N hyper ne coupling constants of 23 nitroxide radicals (Fig. 1) used as the reference were taken from Lebedev et al [68].…”

Structure of Electronically Reduced N-Donor Bidentate Ligands and Their Heteroleptic Four-Coordinate Zinc Complexes: A Survey of Density Functional Theory Results

“…The static electron correlation was quantified by the fractional orbital occupation (FO) as well as integration of the fractional orbital density r FOD over all space (N FOD ). The procedure recommended 105 in the literature (TPSS method, def2-TZVP basis set, Fermi temperature at 5000 K) and successfully employed for open-shell compounds 106 was used to obtain these values. Figure 1 shows the N FOD values for ligands 1-3 and complexes I-II.…”