The Band-Gap Problem in Semiconductors Revisited: Effects of Core States and Many-Body Self-Consistency

TL;DR

This study uses all-electron, self-consistent GW calculations to reveal the significant influence of core states on the quasiparticle gap in semiconductors Si and Ge, challenging previous assumptions and improving theoretical accuracy.

Contribution

It introduces a new paradigm for ab initio quasiparticle theory by demonstrating the importance of core states and self-consistency in GW calculations for real materials.

Findings

Deep-core electrons significantly affect the GW gap in Si.

Neglecting core states can incorrectly predict Si as a semimetal.

Self-consistency enhances the accuracy of quasiparticle gaps and lifetimes.

Abstract

A novel picture of the quasiparticle (QP) gap in prototype semiconductors Si and Ge emerges from an analysis based on all-electron, self-consistent, GW calculations. The deep-core electrons are shown to play a key role via the exchange diagram --if this effect is neglected, Si becomes a semimetal. Contrary to current lore, the Ge 3d semicore states (e.g., their polarization) have no impact on the GW gap. Self-consistency improves the calculated gaps --a first clear-cut success story for the Baym-Kadanoff method in the study of real-materials spectroscopy; it also has a significant impact on the QP lifetimes. Our results embody a new paradigm for ab initio QP theory.