Beyond the random phase approximation with a local exchange vertex

TL;DR

This paper introduces a local-exchange vertex correction based on exact-exchange DFT to systematically improve beyond the GW and RPA methods, unifying various approaches and demonstrating strong results for molecular and condensed matter systems.

Contribution

It develops a local-exchange vertex correction within a unified framework that enhances beyond-RPA electronic structure methods, supported by numerical validation.

Findings

Vertex correction captures key physics similar to Hartree-Fock.

Unified approach improves description of hydrogen and van der Waals bonds.

Demonstrates excellent performance of RPAx methods in energetics.

Abstract

With the aim of constructing an electronic structure approach that systematically goes beyond the GW and random phase approximation (RPA) we introduce a vertex correction based on the exact-exchange (EXX) potential of time-dependent density functional theory. The EXX vertex function is constrained to be local but is expected to capture similar physics as the Hartree-Fock vertex. With the EXX vertex we then consistently unify different beyond-RPA approaches such as the various re-summations of RPA with exchange (RPAx) and the second order screened exchange (SOSEX) approximation. The theoretical analysis is supported by numerical studies on the hydrogen dimer and the electron gas, and we discuss the importance of including the vertex correction in both the screened interaction and the self energy. Finally, we give details on our implementation within the plane-wave pseudo potential framework and demonstrate the excellent performance of the different RPAx methods in describing the energetics of hydrogen and van der Waals bonds.