Orbital Overlap from Multiconfigurational Wavefunctions: A New Way to Explore the Nature of the Metal–Ligand Chemical Bond in Complexes

Chemical bonds are central to understanding molecular structure and reactivity. While Density Functional Theory (DFT) is widely used, systems with complex electronic structures often require multiconfigurational ab initio wavefunctions. This work presents a new implementation of the Overlap (OP/TOP) group of wavefunction-based chemical bond descriptors, extended to multiconfigurational MCSCF wavefunctions. The method provides a framework for investigating chemical bonding across a broad range of systems, including bond dissociation processes, excited electronic states, and coordination compounds containing transition- and f-block metals. Applications demonstrate its ability to characterize changes in overlap density during bond breaking, quantify the effects of dynamic correlation, analyze bonding in excited states, and reveal electronic differences induced by oxidation and Jahn-Teller distortions. These results highlight the versatility of the OP/TOP model as a powerful tool for exploring the nature of chemical bonds in electronically complex systems.