A finite electric-field approach to evaluate the vertex correction for the screened Coulomb interaction in the quasiparticle self-consistent GW method

TL;DR

This paper applies the quasiparticle self-consistent GW method to ionic material slabs under electric field to evaluate vertex corrections in the screened Coulomb interaction, achieving results that agree well with experiments.

Contribution

It introduces a finite electric-field approach within QSGW to evaluate vertex corrections, improving the accuracy of dielectric constant calculations for ionic materials.

Findings

Calculated dielectric constants agree with experimental values.

Large difference between E(Slab) and E(RPA) attributed to vertex corrections.

Supports development of self-consistent G0W methods.

Abstract

We apply the quasiparticle self-consistent GW method (QSGW) to slab models of ionic materials, LiF, KF, NaCl, MgO, and CaO, under electric field. Then we obtain the optical dielectric constants E(Slab) from the differences of the slopes of the electrostatic potential in the bulk and vacuum regions. Calculated E(Slab) show very good agreements with experiments. For example, we have E(Slab)=2.91 for MgO, in agreement with the experimental value E(Experiment)=2.96. This is in contrast to E(RPA)=2.37, which is calculated in the random-phase approximation for the bulk MgO in QSGW. After we explain the difference between the quasiparticle-based perturbation theory and the Greens function based perturbation theory, we interpret the large difference E(Slab)-E(RPA)=2.91-2.37 as the contribution from the vertex correction of the proper polarization which determines the screened Coulomb interaction W. Our result encourages the theoretical development of self-consistent G0W approximation along the line of QSGW self-consistency, as was performed by Shishkin, Marsman and Kresse [Phys. Rev. Lett. 99, 246403(2007)].