Describing strong correlation with fractional-spin correction in density functional theory.

Area of Science:

• Quantum Chemistry
• Computational Materials Science
• Theoretical Physics

Background:

• Standard density functional theory (DFT) approximations struggle with static/strong correlation and delocalization errors.
• Existing methods often fail to accurately describe electronic energy behavior at fractional charges and spins.
• Accurate prediction of molecular properties requires addressing these limitations in DFT functionals.

Purpose of the Study:

• To develop an effective fractional-spin correction for DFT to describe strong correlation.
• To propose a new functional, fractional-spin localized orbital scaling correction (FSLOSC), by combining fractional-spin and fractional-charge corrections.
• To improve the description of electronic energy behavior at fractional charges and spins and reduce delocalization errors.

Main Methods:

• Developed an effective fractional-spin correction method.
• Integrated this correction with the localized orbital scaling correction (LOSC) for fractional-charge.
• Proposed the fractional-spin localized orbital scaling correction (FSLOSC) functional.

Main Results:

• FSLOSC introduces explicit derivative discontinuity and restores flat-plane behavior of electronic energy.
• Improved predictions for ionization potentials, electron affinities, quasiparticle spectra, and reaction barrier heights.
• Correctly described dissociation of ionic/covalent bonds and corrected spurious fractional-charge dissociation in heteroatom molecules.

Conclusions:

• FSLOSC successfully reduces delocalization error and incorporates strong correlation effects within DFT.
• The proposed functional demonstrates significant improvements over conventional DFT approximations.
• FSLOSC offers a low-cost yet accurate approach for describing challenging electronic correlation problems.