Communication: Density functional theory model for multi-reference systems based on the exact-exchange hole...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Kohn-Sham density functional theory (DFT) requires ensemble-state representation for multi-reference electronic ground states using fractionally occupied orbitals.
• Fractional orbital occupation in conventional DFT leads to non-normalized exact-exchange holes and significant fractional-spin errors.

Purpose of the Study:

• To present a straightforward method for incorporating exact-exchange-hole normalization directly into DFT.
• To improve the description of multi-reference systems without compromising accuracy for single-reference systems.

Main Methods:

• Developed a simple approach to directly include exact-exchange-hole normalization within DFT.
• Applied the method to analyze spin-averaged atoms and spin-restricted bond dissociation energy surfaces.

Main Results:

• The proposed model significantly enhances the description of multi-reference systems compared to conventional functionals.
• Accuracy is maintained for single-reference systems.

Conclusions:

• Directly including exact-exchange-hole normalization is an effective strategy for improving DFT calculations of multi-reference systems.
• The method offers a promising avenue for more accurate computational chemistry simulations.