Two-Component Noncollinear Time-Dependent Spin Density Functional Theory for Excited State Calculations

Area of Science:

• Computational Physics
• Quantum Chemistry
• Materials Science

Background:

• Accurate description of electronic excitations is crucial for understanding material properties.
• Existing methods often struggle with noncollinear magnetic systems.
• Kohn-Sham spin density functional theory (DFT) provides a framework for these calculations.

Purpose of the Study:

• To develop a linear response formalism for electronic excitations in noncollinear systems.
• To generalize existing DFT kernels to noncollinear spin density functional theory (TDDFT).
• To enable accurate calculations of spin torque effects in magnetic materials.

Main Methods:

• Introduced auxiliary variables based on density and noncollinear magnetization.
• Generalized common DFT kernels (LDA, GGA, meta-GGA, hybrid) to noncollinear TDDFT.
• Derived functional second derivatives for the noncollinear TDDFT formalism.
• Utilized variational exact-two-component reference with spin-orbit coupling for testing.

Main Results:

• Developed a formalism capable of describing electronic excitations in noncollinear systems.
• The method accounts for all spin magnetization components, regardless of the reference state.
• Achieved a nonzero local exchange-correlation (xc) torque on spin magnetization while preserving global zero-torque theorem.
• Demonstrated the method's capabilities through application to test cases.

Conclusions:

• The presented linear response formalism offers a robust way to study electronic excitations in noncollinear magnets.
• This advancement facilitates more accurate theoretical investigations of spin-related phenomena.
• The method provides a pathway to understanding and predicting the behavior of novel magnetic materials.