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Updated: Nov 23, 2025

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Electron-Nucleus Hyperfine Coupling Calculated from Restricted Active Space Wavefunctions and an Exact Two-Component

Rulin Feng¹, Thomas J Duignan¹, Jochen Autschbach¹

¹Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, United States.

Journal of Chemical Theory and Computation

|January 1, 2021

Summary

This study introduces a new computational method for calculating nuclear hyperfine magnetic properties using exact two-component relativistic operators. This advancement improves accuracy for a wider range of elements in quantum chemistry.

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Area of Science:

Computational Chemistry
Quantum Mechanics
Relativistic Effects

Background:

Accurate calculation of nuclear hyperfine magnetic properties is crucial in chemistry.
Previous methods using nonrelativistic operators had limited applicability, especially for heavy elements.

Purpose of the Study:

To develop and implement an improved computational method for nuclear hyperfine magnetic properties.
To incorporate exact two-component (X2C) relativistic nuclear hyperfine magnetic field operators into ab initio wavefunction calculations.

Main Methods:

Utilized X2C relativistic operators within multireference restricted active space (RAS) calculations.
Treated spin-orbit coupling via RAS state interaction (SO-RASSI).
Implemented the method in the OpenMolcas program.

Main Results:

Successfully calculated electron-nucleus hyperfine coupling constants for various systems.
Demonstrated good agreement with experimental data for main group elements, transition metals, lanthanides, and actinides.
The new method overcomes limitations of previous nonrelativistic approaches.

Conclusions:

The developed X2C relativistic method provides accurate nuclear hyperfine magnetic properties.
This approach significantly expands the applicability of relativistic calculations for hyperfine properties.
Sufficient spin polarization in the active space is key for reliable results.