Communication: Two-determinant mixing with a strong-correlation density functional.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• A novel density functional was recently introduced to address strong electron correlation.
• This functional utilizes symmetry-restricted orbitals to model molecular dissociation limits.

Purpose of the Study:

• To evaluate the performance of the new density functional for describing multi-reference states.
• To demonstrate its accuracy in systems with strong electron correlation, such as avoided crossings.

Main Methods:

• Employing exactly-computed exchange and fractional spin-orbital occupancies.
• Analyzing two-determinant multi-reference states, specifically 50/50 mixtures of symmetry-equivalent Slater determinants.
• Investigating systems at avoided crossings.

Main Results:

• The density functional accurately describes two-determinant multi-reference states.
• The functional's performance was validated using examples involving avoided crossings.
• The connection between multi-reference states and dissociated systems was elucidated.

Conclusions:

• The introduced density functional shows high accuracy for multi-reference states.
• This work validates the functional's capability in capturing complex electronic structures.
• The findings offer a more robust approach to studying strong correlations in molecules.