Fragment-based treatment of delocalization and static correlation errors in density-functional theory

Area of Science:

• Quantum Chemistry
• Computational Materials Science
• Theoretical Physics

Background:

• Modern Kohn-Sham (KS) density-functional theory (DFT) faces challenges in accurately describing systems with fractional electron charges and spins.
• Approximate exchange-correlation functionals in DFT often introduce delocalization and static correlation errors, particularly in bond-stretching processes.

Purpose of the Study:

• To demonstrate an alternative framework, partition density-functional theory (PDFT), for overcoming delocalization and static correlation errors in DFT.
• To improve the accuracy of dissociation energy curves for molecular systems with fractional electron charges and spins.

Main Methods:

• Employed partition density-functional theory (PDFT) using the local density approximation for fragments.
• Performed explicit calculations on systems known to exhibit delocalization and static correlation errors: stretched H2 (+), H2, He2 (+), Li2 (+), and Li2.

Main Results:

• PDFT successfully avoided delocalization and static correlation errors, even with a simple local density approximation for fragments.
• Achieved significantly improved dissociation energy curves for all tested molecular systems.
• The effective KS potential from PDFT solutions exhibited key features near the bond midpoint, absent in standard approximate KS potentials.

Conclusions:

• PDFT offers a robust alternative to standard KS-DFT for systems with fractional electron charges and spins.
• The method provides essential features in the effective potential crucial for accurate electron dynamics and bond-stretching descriptions.
• PDFT significantly enhances the reliability of electronic structure calculations for challenging molecular systems.