Effects from spin-orbit coupling on electron-nucleus hyperfine coupling calculated at the restricted active space...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate calculation of electron-nucleus hyperfine coupling is crucial for understanding molecular electronic structure and magnetic properties.
• Spin-orbit coupling (SO) significantly influences hyperfine interactions, especially in systems containing heavy atoms, but its inclusion in calculations can be computationally demanding.

Purpose of the Study:

• To implement and evaluate a computational method for calculating electron-nucleus hyperfine coupling that explicitly includes spin-orbit coupling (SO) effects.
• To assess the method's applicability to light atomic systems, light ligands in heavy metal complexes, and heavy atoms where unpaired electrons occupy high angular momentum orbitals.
• To investigate the impact of SO coupling on hyperfine coupling tensors in specific molecular systems, such as Neptunium hexafluoride (NpF6).

Main Methods:

• Utilized the restricted active space state interaction (RASSI) method to treat spin-orbit coupling.
• Employed scalar relativistic restricted active space wave functions as the basis for calculations.
• Incorporated spin polarization by defining active orbitals ('ras1', 'ras3') around the principal active space ('ras2').
• Validated the implementation using a benchmark set of Kramers doublet states from molecules containing both light and heavy atoms.

Main Results:

• The implemented method successfully calculates electron-nucleus hyperfine coupling with spin-orbit coupling effects.
• Demonstrated the method's suitability for various systems, including light atoms, light ligands in heavy metal complexes, and heavy atoms with high angular momentum orbitals.
• Detailed investigation of NpF6 revealed that Neptunium (Np) hyperfine coupling is strongly dominated by SO effects.
• Significant SO effects were observed on the Fluorine (F) hyperfine tensor components, including the induction of an isotropic component in the dipolar term.

Conclusions:

• The RASSI-based approach provides an effective means to calculate hyperfine coupling constants, accurately accounting for spin-orbit coupling.
• The method is versatile and applicable to a range of chemical systems, offering valuable insights into magnetic properties.
• The study highlights the critical role of spin-orbit coupling in determining hyperfine interactions for heavy elements and their ligands, as exemplified by NpF6.