Expansão do modelo recobrimento das ligações químicas para funções de onda multiconfiguracionais

Abstract

The description of the electronic structure of a chemical bond is fundamental for all chemical systems, from organic or inorganic reactions to hydrogen interactions in proteins or coordinated bonds in complexes containing lanthanides or actinides. Several theoretical models based on quantum mechanics have been developed and improved to provide a description that better explains how structural changes in molecules affect their ability to form a chemical bond. The overlap model aims to evaluate interactions from the perspective of the shared electronic density between two atoms. Initially, the model had limited applicability to single-electronic-configuration methods. In this work, the equations for obtaining the so-called overlap descriptors were rewritten to expand their applicability to multiconfigurational wavefunctions. Thus, this study comprises the development of new equations for calculating these descriptors, the implementation of this new methodology in the ChemBOS software, and the application of the methodology to generic systems as a proof of concept. A systematic analysis was performed on covalent, ionic, polar covalent, and charge-shift bonds using the CASSCF and DCD−CAS(2) methods for a wide range of molecular systems, including X−O bonds in X−OH (X = H, Li, Na, H2B, H3C, H2N, HO, F) and LiX’ (X’ = F, Cl, and Br). After its expansion, the overlap model demonstrates significant potential for describing chemical bonding, serving as both a complementary and alternative tool to well-established bonding models such as the quantum theory of atoms in molecules (QTAIM). The model was also applied to explain the dissociation profile of the Li−F bond, revealing high sensitivity to ionic/neutral inversion during bond stretching, highlighting its potential to elucidate complex bonding phenomena and offering new possibilities for understanding multiconfigurational chemical bond dynamics. Finally, the model was applied to simple complexes containing lanthanide and actinide metal atoms, demonstrating high sensitivity to the type of bonding observed.