Unconventional materials: the mismatch between electronic charge centers and atomic positions

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Topological quantum chemistry utilizes band representations (BRs) to characterize electronic band structures.
• BRs can be defined by localized orbitals at Wyckoff sites or irreducible representations in momentum space.
• Unconventional materials present a mismatch between average electronic centers and atomic positions.

Purpose of the Study:

• To define and identify unconventional materials based on their band representation characteristics.
• To establish criteria for diagnosing unconventional materials using elementary BRs (eBRs) and atomic-orbital-induced BRs (aBRs).
• To screen for unconventional materials with potential applications.

Main Methods:

• Defining unconventional materials as those whose occupied bands are sums of eBRs but not aBRs.
• Utilizing real-space invariants (RSIs) to describe essential BRs at empty sites.
• Performing high-throughput screening using first-principles calculations.

Main Results:

• Discovery of 423 unconventional compounds.
• Identification of materials with diverse properties including thermoelectrics, topological insulators, electrides, and superconductors.
• Demonstration of an uncompensated total "valence" state in unconventional materials.

Conclusions:

• Unconventional materials possess unique electronic structures characterized by a mismatch between electronic centers and atomic positions.
• The developed framework enables the identification of a wide range of functional materials.
• These findings open avenues for future research into the diverse properties and applications of unconventional materials.