Application of the Adiabatic Connection Random Phase Approximation to Electron-Nucleus Hyperfine Coupling Constants

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Electron-nucleus hyperfine coupling constants are crucial for understanding molecular properties.
• Accurate calculation of these constants is challenging for standard density functional methods.
• Existing methods often require computationally expensive hybrid functionals with large amounts of exact exchange.

Purpose of the Study:

• To investigate the performance of the adiabatic connection random phase approximation (RPA) for calculating electron-nucleus hyperfine coupling constants.
• To assess RPA as a post-Kohn-Sham method for this challenging property.
• To compare RPA with other common computational methods.

Main Methods:

• Application of the adiabatic connection RPA in a post-Kohn-Sham manner.
• Calculation of Fermi-contact and spin-dipole terms.
• Utilizing nonrelativistic and scalar-relativistic exact two-component frameworks.
• Solving a single coupled-perturbed Kohn-Sham equation to obtain the relaxed density matrix.

Main Results:

• RPA significantly improves upon the Kohn-Sham starting point for hyperfine coupling constants.
• RPA shows reduced dependence on the choice of the Kohn-Sham reference functional.
• For main-group systems, RPA outperforms global, range-separated, and local hybrid functionals at comparable computational costs.
• RPA performance is comparable to hybrid functionals for transition-metal compounds and lanthanide complexes.
• Post-Hartree-Fock methods like Møller-Plesset perturbation theory and CC2 perform worse than semilocal density functionals.

Conclusions:

• The adiabatic connection RPA is a computationally efficient and accurate method for electron-nucleus hyperfine coupling constants.
• RPA offers a viable alternative to computationally demanding hybrid functionals, especially for main-group systems.
• The method shows promise for broader application in computational chemistry and spectroscopy.