Density functionals with spin-density accuracy for open shells

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Density Functional Theory (DFT) and spin-DFT (SDFT) are computational methods for studying electron behavior.
• SDFT is often preferred for open-shell systems due to perceived better exchange-correlation (xc) functional approximations and historical DFT limitations.
• Previous DFT applications often used closed-shell approximations, limiting their accuracy for open-shell systems.

Purpose of the Study:

• To evaluate and compare the accuracy of DFT and SDFT for systems without an external magnetic field.
• To demonstrate that corrected DFT approximations can achieve accuracy comparable to SDFT for open-shell systems.
• To establish a theoretical connection between DFT and SDFT in the zero magnetic field limit.

Main Methods:

• Applying corrected DFT approximations to open-shell systems.
• Analyzing the Kohn-Sham (KS) equations within both DFT and SDFT frameworks at zero magnetic field.
• Comparing the performance of approximate xc functionals in DFT and SDFT.

Main Results:

• Correcting DFT for open-shell systems significantly improves its accuracy, matching that of SDFT.
• The KS equations of SDFT can be derived from the generalized KS equations of DFT when the magnetic field is zero.
• An explicit theoretical link between DFT and SDFT is established for the zero magnetic field case.

Conclusions:

• DFT, when properly corrected for open-shell systems, offers comparable accuracy to SDFT for electronic structure calculations.
• The study unifies DFT and SDFT by demonstrating that SDFT is a specific case of generalized DFT in the absence of a magnetic field.
• This finding simplifies theoretical approaches and potentially expands the applicability of DFT methods.