Subsystem density-functional theory for interacting open-shell systems: spin densities and magnetic exchange...

Area of Science:

• Quantum Chemistry
• Computational Materials Science
• Electronic Structure Theory

Background:

• Interacting open-shell systems often adopt high-spin or broken-symmetry (BS) states.
• Describing these states accurately is crucial for understanding magnetic properties and chemical reactivity.
• Conventional Kohn-Sham density-functional theory (KS-DFT) can struggle with convergence for BS states.

Purpose of the Study:

• To investigate the capability of subsystem density-functional theory (sDFT) for describing high-spin and BS states.
• To assess the accuracy of sDFT for spin densities and magnetic coupling constants.
• To identify limitations and potential improvements for sDFT in these applications.

Main Methods:

• Utilizing subsystem density-functional theory (sDFT) with individually defined spin states for constituent systems.
• Employing embedding potentials and monomer basis sets to preserve localized spin states within sDFT.
• Comparing sDFT results for spin densities and magnetic coupling constants against converged KS-DFT calculations.

Main Results:

• sDFT successfully describes high-spin and BS states, yielding spin densities in excellent agreement with KS-DFT.
• sDFT demonstrates improved convergence properties and can resolve cases where KS-DFT fails.
• Magnetic coupling constants from sDFT are accurate when the non-additive kinetic energy is evaluated precisely via potential reconstruction.

Conclusions:

• sDFT provides a robust and accurate framework for studying interacting open-shell systems in high-spin and BS states.
• The method offers advantages in convergence and accuracy over KS-DFT for specific challenging electronic structures.
• Accurate treatment of the non-additive kinetic energy is essential for quantitative prediction of magnetic coupling constants using sDFT.