Chemical bond overlap descriptors from multiconfiguration wavefunctions

Chemical bonds are fundamental in chemistry, serving as the foundation for understanding molecular properties. Over time, various theories and descriptors have evolved to characterize these bonds since the inception of quantum mechanics. This report focuses on extending overlap density and its topological descriptors (OP/TOP) using Multiconfigurational Self-Consistent Field (MCSCF) wavefunctions, highlighting their importance. We present 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 (where X = H, Li, Na, H$_2$B, H$_3$C, H$_2$N, HO, F) and Li$-$X' (where X' = F, Cl, and Br) molecular test systems. CAS(10,16) and CAS(6,20) calculations challenge the MCSCF-based OP/TOP bond descriptors, with comparisons to QTAIM and LVM descriptors. Additionally, we examine the Li--F dissociation profile using OP/TOP descriptors. Our study reveals that chemical bonds formed between atoms with varying electronegativities exhibit overlap density shifted towards the more electronegative atom, as predicted by the OP/TOP descriptors. Quantitative assessments using critical point overlap density and its Laplacian descriptors show reduced spreading in bonds with increasing electronegativity differences. The sensitivity of OP/TOP descriptors to ionic/neutral inversion during Li--F dissociation showcased their potential in elucidating intricate bond phenomena. These insights into multiconfigurational wavefunctions, facilitated by OP/TOP descriptors, open new avenues for understanding chemical bond dynamics across multiconfigurational and multireference wavefunction classes, offering novel applications in the field of chemistry.