Exchange-correlation energy from pairing matrix fluctuation and the particle-particle random phase approximation

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Traditional density functionals struggle with long-range interactions, static correlation, and electron delocalization.
• Existing methods like particle-hole Random Phase Approximation (ph-RPA) show promise but have limitations.

Purpose of the Study:

• To develop and explore novel density functional approximations based on pairing matrix fluctuations.
• To investigate the potential of particle-particle Random Phase Approximation (pp-RPA) for improved electronic structure calculations.

Main Methods:

• Formulation of generalized adiabatic connections for correlation energy using particle-particle (pp-) propagators.
• Numerical implementation and analysis of the lowest-order approximation: pp-RPA.
• Evaluation of pp-RPA performance for various chemical systems, including H2 and H2(+).

Main Results:

• pp-RPA demonstrates size-extensivity, self-interaction freedom, and anti-symmetry.
• Accurate description of strong static correlation and elimination of delocalization errors in relevant systems.
• Competitive non-bonded interaction energies with correct asymptotic decay, outperforming ph-RPA in atomization and reaction energies.

Conclusions:

• Pairing matrix fluctuation-based density functionals offer a promising avenue for future computational chemistry.
• pp-RPA provides a robust framework for addressing limitations of current density functional approximations.
• This work paves the way for more accurate and reliable electronic structure predictions.