A Density Functional Study of Hyperfine Coupling Constants in Steroid Radicals

1999 ◽  
Vol 103 (50) ◽  
pp. 11130-11135 ◽  
Author(s):  
Philippe Lahorte ◽  
Frank De Proft ◽  
Freddy Callens ◽  
Paul Geerlings ◽  
Wim Mondelaers
Keyword(s):  
Density Functional ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Functional Study ◽  
Hyperfine Coupling Constants ◽  
Density Functional Study

Article

1998 ◽  
Vol 76 (12) ◽  
pp. 1817-1826
Author(s):  
Leif A Eriksson ◽  
C Magnus Jansson ◽  
Donald R Arnold ◽  
Russell J Boyd
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Functional Theory ◽  
Hyperfine Coupling Constants ◽  
Isotropic Hyperfine Coupling ◽  
Ionization Processes ◽  
Cleavage Reactions ◽  
Isotropic Hyperfine Coupling Constants

The cleavage reactions of the 1-butene and 4,4-dimethyl-1-pentene molecules and their cations, to form neutral and charged hydrocarbon products, are investigated using hybrid Hartree-Fock/density functional theory. In comparison with previous theoretical results (Du et al.), the density functional cleavage and ionization energies, including zero-point vibrational energy, lie in better agreement with experimental and thermochemical data. Assuming vertical ionization processes the mean absolute deviation (MAD) compared with experiment is 3.4 kcal/mol for the reaction sequences studied. Using adiabatic ionization processes instead gives a MAD of 5.2 kcal/mol. The largest deviation from experiment occurs for the cleavage reactions of the neutral parent molecules, where the difference between theory and experiment is up to 12.8 kcal/mol. In addition to reaction energies we also report optimized ground-state structures, and for the radicals studied, isotropic hyperfine coupling constants that are compared to experimental data. It is found that the experimental hyperfine properties of the 1-butene cation can be explained by rotational averaging caused by the flat potential surface for rotation about the C2-C3 bond.Key words: density functional theory (DFT), alkenes, radical cations, bond cleavage, isotropic hyperfine coupling constants.

scholarly journals First-Principles Calculation of Transition Metal Hyperfine Coupling Constants with the Strongly Constrained and Appropriately Normed (SCAN) Density Functional and its Hybrid Variants

2019 ◽  
Vol 5 (4) ◽  
pp. 69 ◽  
Author(s):  
Dimitrios A. Pantazis
Keyword(s):  
Transition Metal ◽  
First Principles ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
First Principles Calculation ◽  
Chemical System ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Hyperfine Coupling Constants

Density functional theory (DFT) is used extensively for the first-principles calculation of hyperfine coupling constants in both main-group and transition metal systems. As with many other properties, the performance of DFT for hyperfine coupling constants is of variable quality, particularly for transition metal complexes, because it strongly depends on the nature of the chemical system and the type of approximation to the exchange-correlation functional. Recently, a meta-generalized-gradient approximation (mGGA) functional was proposed that obeys all known exact constraints for such a method, known as the Strongly Constrained and Appropriately Normed (SCAN) functional. In view of its theoretically superior formulation a benchmark set of complexes is used to assess the performance of SCAN for the challenging case of transition metal hyperfine coupling constants. In addition, two global hybrid versions of the functional, SCANh and SCAN0, are described and tested. The values computed with the new functionals are compared with experiment and with those of other DFT approximations. Although the original SCAN and the SCAN-based hybrids may offer improved hyperfine coupling constants for specific systems, no uniform improvement is observed. On the contrary, there are specific cases where the new functionals fail badly due to a flawed description of the underlying electronic structure. Therefore, despite these methodological advances, systematically accurate and system-independent prediction of transition metal hyperfine coupling constants with DFT remains an unmet challenge.

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