Insights into the Electronic Structure of Molecules from Generalized Valence Bond Theory

Abstract

In this article we describe the unique insights into the electronic structure of molecules provided by generalized valence bond (GVB) theory. We consider selected prototypical hydrocarbons as well as a number of hypervalent molecules and a set of first- and second-row valence isoelectronic species. The GVB wave function is obtained by variationally optimizing the orbitals and spin coupling in the valence bond wave function. The GVB wave function is a generalization of the Hartree–Fock (HF) wave function, lifting the double occupancy restriction on a subset of the HF orbitals as well as the associated orthogonality and spin coupling constraints. The GVB wave function includes a major fraction (if not all) of the nondynamical correlation energy of a molecule. Because of this, GVB theory properly describes bond formation and can answer one of the most compelling questions in chemistry: How are atoms changed by molecular formation? We show that GVB theory provides a unified description of the nature of the bonding in all of the above molecular species as well as contributing new insights into the well-known, but poorly understood, first-row anomaly.

The nature of the chemical bond in Be2+, Be2, Be2−, and Be3

“…There is an upsurge of interest lately for the description of the chemical bond through a GVB/SC analysis. 15 The Dunning group in its quest to explain hypervalency has introduced the concept of recoupled pair bonds 15(a) and recoupled pair bond dyads, 15(b) being in essence an evolution of the different spin functions during bond formation, and attributed to them the status of an "essential new unifying concept in chemistry." 14 Although not explicitly stated in their work, it is the excited states of the constituent fragments that "do" the job and explain the concept.…”

Hybrid Atomic Orbitals in Organic Chemistry. Part 2: Critique of Practical Aspects

“…Much ink has been spilt over the mathematical equivalency of t and s-p bonds 18 and their use in various contexts. 19 We remind the reader, however, that these models are modern constructs, using modern computational software; there is no conflict with the use of t or s-p bonds in any advanced research project. We continue in this section to examine how each system is limited in its own way.…”

Hybrid Atomic Orbitals in Organic Chemistry. Part 2: Critique of Practical Aspects

“…Let us investigate the use of the three systems of hybridization -sp 3 t hybrids, special hybrids and non-integral hybrids --and compare their utility. Much ink has been spilt over the mathematical equivalency of t and s-p bonds (Palke, 1986) and their use in various contexts (Dunning, Xu, Takeshita, & Lindquist, 2016). We remind the reader, however, that these models are modern constructs, using modern computational software; there is no conflict with the use of t or s-p bonds in any advanced research project.…”