Chemical bonds through probability scattering: Information channels for intermediate-orbital stages

摘要

The information-theoretic (IT) approach to chemical bonds, based upon the molecular probability-scattering channels in orbital resolution, is developed to cover both the overall promotion of atomic orbitals (AO) and the partial communication systems due to typical intermediate stages of reconstructing the system electronic structure, due to the orbital hybridization, orthogonalization, mixing into the molecular orbitals (MO), etc. The geometric and physical orbital promotion channels are distinguished, with the former taking into account solely the elementary channels due to the orbital-mixing, and the latter additionally including the MO-occupation term, which effectively projects-out the orbital promotion via the occupied MO only. This IT development generates the complementary descriptors of the molecular communication channel, viz., its conditional entropy (IT-covalency) and mutual-information (IT-ionicity), which add up to the total IT bond-order. These components provide a transparent description of the covalent/ionic competition for the valence electrons of constituent atoms. Their orbital-promotion contributions, from the elementary sub-channels reflecting the familiar intermediate stages of the bond-formation process, offer a novel information-scattering perspective on the relative roles played by these partial transformations of orbitals in shaping the resultant entropy/information descriptors of the system chemical bonds. The combination (grouping) rules for the consecutive and parallel arrangements of the elementary sub-channels are summarized and the stage-additivity of the IT bond- descriptors in the molecular sequential cascade of the elementary sub-channels for the intermediate sets of orbitals is examined in a more detail. A distinction between the molecular information channels describing the separated atoms and the free-atoms in the system atomic promolecule, respectively, is stressed and their entropy/information descriptors are briefly summarized. The associated difference descriptors of the overall IT bond-orders with respect to the promolecular reference are introduced and similar displacement measures are designed for the molecular promotion of intermediate orbitals. The illustrative results for the simplest model of a single chemical bond originating from an interaction between two overlapping atomic orbitals are presented. In particular, the bond-increments due to the orthogonalization and de-orthogonalization sub-channels of the overall AO-promotion cascade will be investigated.