Crystal Orbital Bond Index: Covalent Bond Orders in Solids

The crystal orbital bond index (COBI) is a new and intuitive method for quantifying covalent bonding in solid-state materials. COBI is based on the bond index by Wiberg and Mayer and extends their ideas to the case of translationally invariant objects, that is, crystalline matter. COBI's qualitative interpretation resembles the well-established crystal orbital overlap population and crystal orbital Hamilton population methods but should be more familiar to chemists since it directly relates to the classical bond order. In contrast to the aforementioned descriptors, COBI also allows for examining multicenter interactions within a local-orbital framework. As an additional bonding indicator, we refer to the Ewald sum for electrostatic lattice potentials, thereby enabling the calculation of electrostatic lattice energies as well as site potentials from quantum-mechanical charges as directly derived from the wave function, not from the density.

Automated summary

COBI is a new method for quantifying covalent bonding in solid-state materials, providing a more intuitive approach to examining multicenter interactions. It calculates electrostatic lattice energies directly from the wave function, related to classical bond order.