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Physical Spin Torques from Exactly Constrained Exchange-Correlation Torques
Jacques K Desmarais1, Kamel Bencheikh2, Giovanni Vignale3
1Università di Torino, Dipartimento di Chimica, via Giuria 5, 10125 Torino, Italy.
Physical Review Letters
|January 26, 2026
Summary
This study introduces Spin-current DFT to accurately capture physical spin torques in noncollinear magnetic systems. It resolves spurious exchange-correlation torques, enabling precise spin dynamics simulations.
Area of Science:
- Condensed Matter Physics
- Quantum Mechanics
- Materials Science
Background:
- Spin-density functional theory (SDFT) struggles to accurately model physical spin torques in noncollinear magnetic systems.
- SDFT's limitations include spurious exchange-correlation torques and the inability to rigorously incorporate vector potentials and spin-orbit couplings.
Purpose of the Study:
- To develop a robust theoretical framework for capturing physical spin torques in noncollinear magnetism.
- To overcome the limitations of SDFT in describing spin dynamics.
Main Methods:
- Propose a solution utilizing the U(1)×SU(2) invariance of the exchange-correlation energy within Spin-current DFT.
- Leverage an exact constraint not accessible to standard SDFT.
Main Results:
- Achieve nonvanishing exchange-correlation torques on noncollinear solutions that are constrained by internal symmetry.
- Demonstrate that these constrained torques do not affect spin magnetization propagation.
Conclusions:
- Spin dynamics are accurately described by physical currents and physical spin torques alone.
- The proposed Spin-current DFT approach provides a rigorous method for studying spin torques in complex magnetic systems.
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