A new take on interpreting chemical bond analysis in solids

Researchers from Skoltech, SberUniversity, the M.N. Mikheev Institute of Metal Physics of RAS, and Ural Federal University have published a review paper in the Russian Chemical Reviews, introducing a novel method to interpret chemical bonding in solids. This approach, which builds upon the Wannier function concept, offers a way to reconcile rigorous calculations with intuitive, chemist-friendly explanations of bonding.

Traditionally, chemists rely on orbitals and qualitative characteristics like ionicity, covalency, and charge transfer to understand bonding. However, in crystals, orbitals become smeared out across multiple atoms and depend on the wave vector, leading to an infinite number of orbitals within a single band. The Wannier function, introduced in 1937, resolves this issue by enabling localized orbitals around individual atoms.

The research team has developed a specific technique for constructing Wannier functions, projecting them onto atomic orbitals to preserve symmetry while maintaining localized descriptions. This method allows for the calculation of atomic charges, bond energies, and the differentiation between ionic and covalent interactions based on first-principles results.

One example highlighted in the review is the explanation of the inverted charge distribution in boron phosphide crystals. Contrary to predictions based on electronegativity, boron atoms acquire a negative charge in this compound, an observation confirmed by earlier calculations. The new Wannier function-based approach makes this counterintuitive finding interpretable using clear and meaningful chemical notions, bridging the gap between quantitative analysis and conceptual models of the material.