Spin-orbit coupling from a two-component self-consistent approach. I. Generalized Hartree-Fock theory

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Standard one-component Hartree-Fock and Kohn-Sham methods are limited for systems with strong spin-orbit coupling.
• Treating spin-orbit coupling requires advanced theoretical frameworks beyond simple spin-unrestricted approaches.

Purpose of the Study:

• To develop and implement a self-consistent two-component Hartree-Fock theory for accurate spin-orbit coupling calculations.
• To extend the CRYSTAL program for molecular calculations involving complex Fock and density matrices.
• To enable the study of noncollinear magnetism and orbital current densities.

Main Methods:

• Generalization of Hartree-Fock theory to a two-component spinor formalism.
• Molecular implementation within the CRYSTAL program, extending one-component code.
• Handling complex Fock and density matrices, including off-diagonal spin blocks.
• Development of a novel scheme for imposing noncollinear magnetization as an initial guess.

Main Results:

• The two-component formalism successfully incorporates spin-orbit coupling effects.
• The implementation handles complex matrices and off-diagonal spin blocks for open-shell systems.
• The new scheme for initial magnetization improves convergence and avoids local minima.
• Accurate treatment of local magnetic torque, noncollinear magnetization, and orbital current-density is achieved.

Conclusions:

• The developed two-component Hartree-Fock method provides a robust framework for electronic structure calculations with spin-orbit coupling.
• This approach is crucial for accurately modeling materials exhibiting complex magnetic properties.
• The method facilitates convergence to ground-state solutions in challenging electronic configurations.