Exchange-Correlation Energy from Pairing Matrix Fluctuation and the Particle-Particle Random Phase Approximation

TL;DR

This paper introduces a new approach to calculating exchange-correlation energy using pairing matrix fluctuation, highlighting the advantages of the particle-particle RPA in addressing various electronic structure challenges.

Contribution

It formulates an adiabatic connection based on pairing interactions and demonstrates the benefits of the particle-particle RPA in density functional theory.

Findings

No delocalization error with fractional charges

Accurately describes van der Waals interactions

Eliminates static correlation error in single-bond systems

Abstract

We formulate an adiabatic connection for the exchange-correlation energy in terms of pairing matrix fluctuation. This connection opens new channels for density functional approximations based on pairing interactions. Even the simplest approximation to the pairing matrix fluctuation, the particle-particle Random Phase Approximation (pp-RPA), has some highly desirable properties. It has no delocalization error with a nearly linear energy behavior for systems with fractional charges, describes van der Waals interactions similarly and thermodynamic properties significantly better than particle-hole RPA, and eliminates static correlation error for single-bond systems. Most significantly, the pp-RPA is the first known functional that has an explicit and closed-form dependence on the occupied and unoccupied orbitals and captures the energy derivative discontinuity in strongly correlated systems. These findings illlustrate the potential of including pairing interactions within a density functional framework.