Tight-Binding Models for Lone Pair, Heteroanionic Solids, and Application to Layered Oxyhalides

TL;DR

This paper introduces a methodology using Wannier-based tight-binding models to analyze complex bonding in heteroanionic and lone pair materials, exemplified by BiOCl and Bi2YO4Cl, with applications in understanding electronic features and photostability.

Contribution

The paper presents a novel approach to dissect electronic properties of complex materials by combining Wannier functions, symmetry enforcement, and orbital manipulation, applicable to various functional materials.

Findings

Identified the role of Bi lone pairs in photoluminescence.

Analyzed how crystal structure affects photostability.

Demonstrated the methodology on BiOCl and Bi2YO4Cl.

Abstract

We provide a methodology to understand materials with complex bonding patterns, and apply it to the example of heteroanionic and lone pair materials. We build a tight-binding model based on Wannier functions fitted on density functional theory results, followed by enforcing symmetry on the atomic orbital basis set, and finally connecting and disconnecting sets of orbitals from the tight-binding model to understand their individual contribution to the resulting materials properties. We apply this methodology to complex materials, namely BiOCl and Bi$_2$YO$_4$Cl - part of a broader class of materials investigated for their applications in photocatalysis and photoluminescence. Our methodology can be generalized and applied to a wide variety of other materials, including halide perovskites, and multiferroic materials. This methodology allows us to isolate the origin of key electronic features in these materials, including the role of the Bi lone pair-anion bonding interaction - key to photoluminescence in many materials. Finally, we investigate the role of the crystal structure, Chlorine and Oxygen orbital energy levels and bonding in determining the photostability of bismuth oxyhalides. Our methodology allows us to understand the functionality of complex materials in an intuitive and qualitative manner.