Spin-orbit couplings within spin-conserving and spin-flipping time-dependent density functional theory:...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Spin-orbit couplings (SOCs) are crucial for understanding molecular properties and reactivity.
• Accurate computation of SOCs is challenging, especially within time-dependent density-functional theory (TD-DFT).

Purpose of the Study:

• To implement and validate a new computational protocol for SOCs within TD-DFT.
• To assess the performance of the new method for various molecular systems, including organic molecules, diradicals, and single-molecule magnets.

Main Methods:

• Employed a time-dependent density-functional theory (TD-DFT) framework with both spin-conserving and spin-flip (SF-TD-DFT) formulations.
• Utilized the Breit-Pauli Hamiltonian and Wigner-Eckart's theorem for SOC matrix element calculations.
• Computed SOCs using zero-order non-relativistic states and a state-interaction procedure.

Main Results:

• The new SOC protocol demonstrated efficiency across benchmark calculations for organic molecules, diradicals, and a single-molecule magnet.
• SOCs in organic molecules were found to be insensitive to functional or basis set choices.
• Spin-flip TD-DFT (SF-TD-DFT) results for diradicals showed significant functional dependence.
• Calculated spin-reversal energy barrier for an Fe(III) single-molecule magnet using non-collinear SF-TD-DFT showed good agreement with experimental data.

Conclusions:

• The developed TD-DFT protocol provides an efficient and accurate method for computing spin-orbit couplings.
• The findings highlight the importance of functional choice in SF-TD-DFT for systems with significant spin interactions.
• The method shows promise for accurate prediction of magnetic properties in molecular materials.