CNDO/SP calculation of<i>g</i>-tensors of free radicals

Чувылкин, Н. Д.; Zhidomirov, G. M.

doi:10.1080/00268977300101071

Cited by 33 publications

(4 citation statements)

References 22 publications

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“…Upon irradiation with UV light, several EPR signals appeared with a central g value of 2.0045, which was consistent with the value of the free electron of 2.0023. 34–36 Time dependent EPR spectra showed the details of signal evolution and hyperfine splitting (Fig. 2c).…”

Section: Resultsmentioning

confidence: 95%

Manipulating D–A interaction to achieve stable photoinduced organic radicals in triphenylphosphine crystals

et al. 2023

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Section: Resultsmentioning

confidence: 95%

Manipulating D–A interaction to achieve stable photoinduced organic radicals in triphenylphosphine crystals

et al. 2023

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“…where "occ" and "unocc" refer to the Ag contributions from occupied and unoccupied MOs, respectively. This parametrization, first introduced by Chuvylkin et al 56 for the calculation of Agtj of various hydrocarbon radicals on the basis of the CNDO method (these authors used a more restrictive parametrization with A0" = Aunocc = 4), gives considerably improved results. We found A0** = 3, Aunocc = 1 to give the best fit to the experimental values of Agxx and Agyy (results given in Table I).…”

Section: B0mentioning

confidence: 99%

3-mm High-field EPR on semiquinone radical anions Q.cntdot.- related to photosynthesis and on the primary donor P.cntdot.+ and acceptor QA.cntdot.- in reaction centers of Rhodobacter sphaeroides R-26

Burghaus¹,

Plato²,

Rohrer³

et al. 1993

J. Phys. Chem.

225

281

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W-band EPR (A = 3 mm, v =S 95 GHz) investigations of frozen solutions of various semiquinone anion radicals in vitro are presented. Among the quinones studied are ubiquinone-10 and the primary electron acceptors of photosystem I and I1 of plant photosynthesis, vitamin K1, and plastoquinone-9, respectively. In addition, W-band spectra of the primary quinone QA*-and of the radical pair Pi&Q,'-in Zn-substituted reaction centers of Rhodobacter sphaeroides R-26 are shown. The electron Zeeman interaction at resonant Bo fields in the W-band is increased by a factor of 10 as compared with conventional X-band, leading to almost completely resolved g-tensor components in all quinone radicals. By means of computer simulations of the EPR spectra of the immobilized radical ions, anisotropic g tensor components, anisotropic line width contributions, and, in some cases, hyperfine tensor information could be obtained. The data are partially interpreted by semiempirical MO methods including solvent effects. In all quinone radical anions studied, the measured g-tensor components are assigned to the molecular axes as follows: gxx > gYY > g,,, where x is along the C-O bond direction and z is perpendicular to the quinone plane.

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“…It is therefore not surprising that the calculation of EPR g tensors of molecules and metal complexes from first principles and using semiempirical methods has a long history. Earlier attempts to get a theoretical handle on the g tensor were based on semiempirical methods; for instance, Hückel theory and variants thereof, − or the semiempirical Hartree–Fock (HF) approximations INDO − and CNDO. − The connection between the spin-Hamiltonian and first-principles electronic structure theory can be made with the help of perturbation theory and the use of partitioning techniques. , In earlier g tensor calculations, a major focus was on assessing the importance of approximations made in second order perturbation calculations, the problem of gauge invariance, the importance of two-electron spin–orbit and spin-other-orbit terms, or contributions from higher order terms . Among the earliest g tensor calculations using HF theory and including all the spin–orbit terms as a perturbation were those by Moores and McWeeny .…”

Section: Introductionmentioning

confidence: 99%

Variational versus Perturbational Treatment of Spin–Orbit Coupling in Relativistic Density Functional Calculations of Electronic g Factors: Effects from Spin-Polarization and Exact Exchange

Verma

Autschbach

2013

J. Chem. Theory Comput.

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Different approaches are compared for relativistic calculations of electronic g factors of molecules with light atoms, transition metal complexes, and selected complexes with actinides, using density functional theory (DFT) and Hartree-Fock (HF) theory. The comparison includes functionals with range-separated exchange. Within the variationally stable zeroth-order regular approximation (ZORA) relativistic framework, g factors are obtained with a linear response (LR) method where spin-orbit (SO) coupling is treated as a linear perturbation, a spin-polarized approach based on magnetic anisotropy (MA) that includes SO coupling variationally, and a quasi-restricted variational SO method previously devised by van Lenthe, van der Avoird, and Wormer (LWA). The MA and LWA approaches were implemented in the open-source NWChem quantum chemistry package. We address the importance of electron correlation (DFT vs HF), the importance of including spin polarization in the g tensor methodology, the question of whether the use of nonrelativistic spin density functionals is adequate for such calculations, and the importance of treating spin-orbit coupling beyond first-order. For selected systems, the extent of the DFT delocalization error is explicitly investigated via calculations of the energy as a function of fractional electron numbers. For a test set of small molecules with light main group atoms, all levels of calculation perform adequately as long as there is no energetic near-degeneracy among occupied and unoccupied orbitals. The interplay between different factors determining the accuracy of calculated g factors becomes more complex for systems with heavy elements such as third row transition metals and actinides. The MA approach is shown to perform acceptably well for a wide range of scenarios.

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CNDO/SP calculation ofg-tensors of free radicals

Cited by 33 publications

References 22 publications

Manipulating D–A interaction to achieve stable photoinduced organic radicals in triphenylphosphine crystals

Manipulating D–A interaction to achieve stable photoinduced organic radicals in triphenylphosphine crystals

3-mm High-field EPR on semiquinone radical anions Q.cntdot.- related to photosynthesis and on the primary donor P.cntdot.+ and acceptor QA.cntdot.- in reaction centers of Rhodobacter sphaeroides R-26

Variational versus Perturbational Treatment of Spin–Orbit Coupling in Relativistic Density Functional Calculations of Electronic g Factors: Effects from Spin-Polarization and Exact Exchange

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