Chirality-Induced Spin Selectivity: Analysis of Density Functional Theory Calculations

Area of Science:

• Condensed matter physics
• Quantum chemistry
• Materials science

Background:

• Chirality-induced spin selectivity (CISS) is a phenomenon where chiral materials transport electrons with different spin orientations at different rates.
• While CISS has been observed in various systems, a complete theoretical understanding, especially concerning device interfaces and computational accuracy, is lacking.

Purpose of the Study:

• To investigate the factors influencing spin-polarization in chiral materials using first-principles calculations.
• To evaluate the impact of system-electrode interfaces, spin-orbit coupling methods, and exchange-correlation functionals on CISS.
• To assess the role of bias and spin-flip terms in CISS phenomena.

Main Methods:

• Density functional theory (DFT) combined with spin-orbit coupling (SOC).
• In-house electron transport program for zero-bias calculations.
• Nonequilibrium Green's function (NEGF) formalism using Quantum Atomistix Toolkit (Q-tool) for bias-dependent calculations.
• Investigation of helical oligopeptide, chiral gold cluster, and helicene model systems.

Main Results:

• Spin-polarization magnitude is sensitive to the chiral system-electrode interface modeling.
• The choice of SOC calculation method and exchange-correlation functional significantly affects spin-polarization.
• Spin-flip terms are potentially important for accurate CISS effect calculations, especially under bias.

Conclusions:

• First-principles calculations provide valuable intrinsic responses for understanding CISS.
• Further theoretical development is needed to fully resolve CISS phenomena in comparison with experimental results.
• The study highlights the importance of interface effects and computational choices in modeling CISS.