Subsystem density-functional theory: A reliable tool for spin-density based properties.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Open-shell radical systems (e.g., organic crystals, proteins, DNA) present computational challenges.
• Correlated ab initio wave function methods are computationally expensive.
• Standard Kohn-Sham DFT struggles with overdelocalization in radical systems.

Purpose of the Study:

• To review the capabilities of subsystem density-functional theory (DFT) for open-shell systems.
• To identify open questions and future research directions.
• To highlight applications in spin-dependent properties.

Main Methods:

• Subsystem DFT methods are presented as a computationally efficient alternative.
• The approach avoids hard constraints on electron density.
• It preserves predefined subsystem spin-patterns by starting from isolated fragment densities.

Main Results:

• Subsystem DFT provides a pragmatic solution to the overdelocalization problem.
• It is less computationally demanding than correlated ab initio methods.
• The methods are crucial for describing open-shell properties.

Conclusions:

• Subsystem DFT is a rapidly developing and important tool for open-shell systems.
• Further development is needed for challenging future applications.
• The focus is on advancing spin-dependent property calculations.