Describing static correlation in bond dissociation by Kohn-Sham density functional theory

Area of Science:

• Quantum Chemistry
• Computational Materials Science

Background:

• Density functional theory (DFT) is a powerful tool for electronic structure calculations.
• Accurate description of bond dissociation, especially in simple systems like H(2), is crucial for developing reliable theoretical methods.
• The random phase approximation (RPA) is a method for approximating the exchange-correlation energy in DFT.

Purpose of the Study:

• To evaluate the performance of DFT with RPA for describing H(2) bond dissociation.
• To investigate the limitations of RPA and RPA+X (RPA with exact exchange) in capturing static correlation and ensuring size consistency.
• To analyze the role of double excitations in adiabatic linear response theory.

Main Methods:

• Spin-restricted Kohn-Sham formalism.
• Random Phase Approximation (RPA) for exchange-correlation energy.
• Adiabatic Connection Curves (ACC) analysis.
• RPA with exact exchange kernel (RPA+X) calculations.

Main Results:

• RPA provides a correct description of H(2) bond dissociation in a spin-restricted formalism.
• Strong curvature in ACC at large bond lengths indicates significant static correlation, highlighting limitations of hybrid functionals.
• RPA and RPA+X exhibit unphysical repulsion at finite but large bond lengths.
• RPA+X is found to be not size consistent, unlike RPA.

Conclusions:

• RPA is a viable method for H(2) bond dissociation, but has limitations at larger bond lengths.
• The unphysical repulsion in RPA and RPA+X may stem from the absence of double excitations in adiabatic linear response theory.
• Further theoretical developments are needed to address the limitations of current methods for describing bond dissociation accurately.