Relativistic spin-orbit effects on hyperfine coupling tensors by density-functional theory

Area of Science:

• Quantum Chemistry
• Computational Physics
• Spectroscopy

Background:

• Hyperfine coupling tensors are crucial for understanding molecular electronic structure and magnetic properties.
• Accurate theoretical calculations of these tensors are essential for interpreting experimental data.

Purpose of the Study:

• To implement and validate a second-order perturbation theory for spin-orbit corrections to hyperfine coupling tensors within a density-functional framework.
• To assess the accuracy of all-electron and pseudopotential approaches for calculating these corrections.
• To investigate the performance of exchange-correlation functionals for nonrelativistic contributions.

Main Methods:

• Density-functional theory (DFT) with second-order perturbation theory for spin-orbit (SO) corrections.
• Incorporation of one- and two-electron SO interactions using all-electron atomic mean-field approximation and/or SO pseudopotentials.
• Combination of DFT results with ab initio coupled-cluster singles and doubles with perturbative triples (CCSD(T)) for first-order contributions.

Main Results:

• Good agreement between all-electron and pseudopotential results for lighter nuclei, except when scalar relativistic effects are significant.
• Identified limitations of current exchange-correlation functionals in accurately reproducing the nonrelativistic Fermi contact term.
• Demonstrated that spin-orbit corrections improve agreement with experimental hyperfine coupling constants when significant.

Conclusions:

• The developed method provides a reliable approach for calculating spin-orbit corrections to hyperfine coupling tensors.
• The study highlights the importance of considering spin-orbit interactions for accurate hyperfine coupling predictions.
• Antisymmetric contributions and rovibrational effects were discussed for specific molecular systems.