Application of topological quantum chemistry in electrides

TL;DR

This paper applies topological quantum chemistry (TQC) to identify electrides by analyzing band representations and orbital characters, revealing their unconventional ionic nature and aiding in discovering new electride materials.

Contribution

It demonstrates how TQC can effectively identify electrides through band representation analysis, highlighting their unique electronic structure involving vacancy-centered pseudo-orbitals.

Findings

Electrides exhibit band representations not decomposable into atomic-orbital-induced bands.

Floating bands in electrides are associated with pseudo-orbitals at vacancies.

TQC provides a new method to discover and analyze electrides in ionic crystals.

Abstract

The recently developed theory of topological quantum chemistry (TQC) has built a close connection between band representations in momentum space and orbital characters in real space. It provides an effective way to diagnose topological materials, leading to the discovery of lots of topological materials after the screening of all known nonmagnetic compounds. On the other hand, it can also efficiently reveal spacial orbital characters, including average charge centers and site-symmetry characters. By using TQC theory with the computed irreducible representations in the first-principles calculations, we demonstrate that the electrides with excess electrons serving as anions at vacancies can be well identified by analyzing band representations (BRs), which cannot be expressed as a sum of atomic-orbital-induced band representations (aBRs). In fact, the floating bands (formed by the excess electrons) belong to the BRs induced from the "pseudo-orbitals" centered at vacancies. In other words, the electrides are proved to be unconventional ionic crystals, where a set of occupied bands is not a sum of aBRs but necessarily contains a BR from vacancies. The TQC theory provides a promising avenue to pursue more electride candidates in ionic crystals.