Separation of energies of the direct (through-space) and indirect (through-bridge) interactions in SCF LCAO MO theory

Within the standard SCF LCAO MO theory the electronic energy is partitioned into components associated with pairs of atomic orbitals and contributions due to the direct (through‐space) and indirect (through‐bridge) chemical bonds in molecules are identified. Conditions for the overall bonding effect of the implicit bridge interactions are qualitatively examined using the simplest case of the three‐orbital model and possible extensions including electron correlation are briefly commented upon. © 2012 Wiley Periodicals, Inc. The direct (“through‐space”) bonding interaction between neighboring atoms implies the presence of the bond‐charge between the two nuclei. For more distant atomic partners, e.g. in cross‐ring p‐interactions, such an accumulation of the valence electrons can be absent, and an indirect (“throughbridge”) mechanism is needed. This article introduces a recipe for partitioning the molecular electronic energy into components associated with pairs of atomic orbitals and identifying the contributions of the direct and indirect chemical bond types.