Vibrational properties and bonding nature of Sb₂Se₃ and their implications for chalcogenide materials

Antimony selenide (antimonselite, Sb₂Se₃) is a versatile functional material with emerging applications in solar cells. It also provides an intriguing prototype to study different modes of bonding in solid chalcogenides, all within one crystal structure. In this study, we unravel the complex bonding nature of crystalline Sb₂Se₃ by using an orbital-based descriptor (the crystal orbital Hamilton population, COHP) and by analysing phonon properties and interatomic force constants. We find particularly interesting behaviour for the medium-range Sb···Se contacts, which still contribute significant stabilisation but are much softer than the "traditional" covalent bonds. These results have implications for the assembly of Sb₂Se₃ nanostructures, and bond-projected force constants appear as a useful microscopic descriptor for investigating a larger number of chalcogenide functional materials in the future.