SCF MO INDO calculation of g-tensors of some ?-type radicals

Articles you may be interested inMassively parallel implementations of coupled-cluster methods for electron spin resonance spectra. I. Isotropic hyperfine coupling tensors in large radicals Density functional calculations of molecular g -tensors in the zero-order regular approximation for relativistic effectsThe results of calculations of doublet state G tensors of organic radicals often show unsatisfactory agreement with the respective experimental data. This led us to reconsider the results of the Rayleigh-Schrödinger perturbation theory approach found in the literature. We came to the conclusion that neither the expressions given for restricted nor for unrestricted Hartree-Fock functions are fully correct. In this paper new expressions for the G tensor to be used with restricted Hartree-Fock functions will be introduced and results of calculations employing these new formulas in conjunction with molecular states from semiempirical Hartree-Fock-type calculations are discussed.

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“…These expressions are in agreement with the literature, 11,3,5 where a somewhat different approach is used in the derivation.…”

Section: ͑10͒supporting

confidence: 89%

“…[3][4][5][6][7][8] Unfortunately, the results of such calculations using Hartree-Fock-type molecular orbitals are often found to be less than satisfactory. This led us to reconsider the theoretical background of this approach.…”

Section: Introductionmentioning

confidence: 99%

On the calculation of G tensors of organic radicals

Törring

Knüpling

et al. 1997

The Journal of Chemical Physics

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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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“…However, concrete applications are very scarce and as a rule they have to do with s-electron radicals [2][3][4]. Only recently the first systematic calculations of g-tensors of a-type radicals were performed within the scope of all-valence-electron INDO method [5].…”

Section: Molecular Physics: An International Journal At the Interfacementioning

confidence: 99%