The Chemical Bond as a Manifestation of Quantum Mechanical Interference: Theory and Applications of the Interference Energy Analysis Using SCGVB Wave Functions

The Interference Energy Analysis (IEA), based on the Generalized Product Function Energy Partitioning method (GPF-EP), is presented and applied to a variety of molecules exhibiting distinct chemical bond patterns: 2c–1e, 2c–2e, 3c–2e bonds. This method makes use of an Independent Particle Model (IPM) and of Spin-Coupled Generalized Valence Bond (SCGVB) wavefunctions to obtain the atomic-like orbitals. The analysis of the chemical bonds using the GPF-EP approach has shown that quantum interference is the effect responsible for the formation of all types of bonds considered, irrespective of the number of centers or of electrons involved in the bond and of the nature of the atoms. Therefore, quantum interference provides a solid framework to unify the concept of chemical bond. From the quantum interference perspective, the minimum requirement for a chemical bond to be formed is one electron and two interfering one-electron states belonging to different atoms. Furthermore, the traditional way of classifying the type of bond based on the difference of electronegativity of the atoms (Δχ), as covalent (Δχ ≈ 0), polar (Δχ small) and ionic (Δχ ≥ 1.9), obscures the fact that all bonds result from the same quantum effect.