jp7b07054_si_001.pdf (548 kB)
Identification and Characterization of Molecular Bonding Structures by ab initio Quasi-Atomic Orbital Analyses
journal contribution
posted on 2017-11-14, 18:51 authored by Aaron C. West, Juan J. Duchimaza-Heredia, Mark S. Gordon, Klaus RuedenbergThe quasi-atomic analysis of ab initio electronic wave functions in full valence spaces,
which was developed in preceding papers, yields oriented quasi-atomic
orbitals in terms of which the ab initio molecular
wave function and energy can be expressed. These oriented quasi-atomic
orbitals are the rigorous ab initio counterparts
to the conceptual bond forming atomic hybrid orbitals of qualitative
chemical reasoning. In the present work, the quasi-atomic orbitals
are identified as bonding orbitals, lone pair orbitals, radical orbitals,
vacant orbitals and orbitals with intermediate character. A program
determines the bonding characteristics of all quasi-atomic orbitals
in a molecule on the basis of their occupations, bond orders, kinetic
bond orders, hybridizations and local symmetries. These data are collected in a record and provide the information for a comprehensive
understanding of the synergism that generates the bonding structure
that holds the molecule together. Applications to a series of molecules
exhibit the complete bonding structures that are embedded in their ab initio wave functions. For the strong bonds in a molecule,
the quasi-atomic orbitals provide quantitative ab initio amplifications of the Lewis dot symbols. Beyond characterizing strong
bonds, the quasi-atomic analysis also yields an understanding of the
weak interactions, such as vicinal, hyperconjugative and radical
stabilizations, which can make substantial contributions to the molecular
bonding structure.