"Ensemblization" of density functional theory.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Conventional Density Functional Theory (DFT) excels at ground-state electronic structure but struggles with degenerate, mixed, or excited states.
• Existing extensions of DFT often introduce uncontrolled errors and inconsistencies.
• A need exists for a rigorous theoretical framework to address these limitations.

Purpose of the Study:

• Introduce and analyze Ensemble DFT (EDFT) as an in-principle exact theoretical framework.
• Develop a rigorous approach for constructing novel density functionals within the EDFT framework.
• Extend DFT-based methodologies beyond ground-state calculations.

Main Methods:

• Focus on the "ensemblization" of exact and approximate density functionals.
• Develop a rigorous framework for ensemble density functionals.
• Investigate the interplay between symmetry considerations and ensemble properties.

Main Results:

• EDFT provides an exact treatment for electronic states beyond the conventional ground state.
• The "ensemblization" approach leads to novel approximations consistent with the EDFT framework.
• Symmetry and ensemble properties synergize to create practical DFT-based methods for excited and mixed states.

Conclusions:

• EDFT offers a robust and exact alternative to conventional DFT for complex electronic systems.
• The developed methodology extends the applicability of DFT to excited states and other challenging problems.
• This work highlights the necessity of exploring beyond the standard ground-state Kohn-Sham treatment in electronic structure theory.