Chemical Bond Overlap Descriptors From Multiconfiguration Wavefunctions

The chemical bond is a fundamental concept in chemistry, and various models and descriptors have evolved since the advent of quantum mechanics. This study extends the overlap density and its topological descriptors (OP/TOP) to multiconfigurational wavefunctions. We discuss a comparative analysis of OP/TOP descriptors using CASSCF and DCD-CAS(2) wavefunctions for a diverse range of molecular systems, including X–O bonds in X–OH (XH, Li, Na, H₂B, H₃C, H₂N, HO, F) and Li–X′ (XF, Cl, and Br). Results show that OP/TOP aligns with bonding models like the quantum theory of atoms in molecules (QTAIM) and local vibrational modes theory, revealing insights such as overlap densities shifting towards the more electronegative atom in polar bonds. The Li–F dissociation profile using OP/TOP descriptors demonstrated sensitivity to ionic/neutral inversion during Li–F dissociation, highlighting their potential for elucidating complex bond phenomena and offering new avenues for understanding multiconfigurational chemical bond dynamics.