Spin-Multiplet Components and Energy Splittings by Multistate Density Functional Theory.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Kohn-Sham density functional theory (KS-DFT) is widely used but struggles with spin-multiplet energy degeneracy.
• Accurate description of spin states is crucial for understanding chemical and physical phenomena.

Purpose of the Study:

• To develop a novel computational method for accurately determining multiplet energies.
• To address the limitations of existing density functional approximations in describing spin-state energetics.
• To provide a rigorous approach for electronic coupling in multiconfigurational systems.

Main Methods:

• Introduction of multistate density functional theory (MSDFT) as a hybrid quantum mechanical approach.
• MSDFT treats wave functions, electron densities, and energy functionals on an equal footing for various electronic states.
• Application of MSDFT to valence excitations in atoms and molecules.

Main Results:

• MSDFT successfully represents spin-multiplet components and determines their energies.
• A key finding is the rigorous definition of the transition density functional in MSDFT for electronic coupling.
• The method is validated through applications to atomic and molecular valence excitations.

Conclusions:

• MSDFT offers a robust framework for calculating spin-multiplet energies and electronic coupling.
• The developed methodology can guide the design and optimization of transition density functionals.
• This work advances the capability of density functional theory for complex electronic structure problems.