Reduced communication channels of molecular fragments and their entropy/information bond indices

Abstract

A reduction of the molecular “communication channel” in atomic resolution, which generates the entropy/information indices of the system chemical bonds, is performed by combining several atomic inputs and/or outputs into a single unit representing a collection of bonded atoms. The implications of such fragment-reduced communication channels for gaining both the internal (intra-subsystem) and external (inter-subsystem) bond-indices are examined. The entropy/information quantities of the reduced channels of molecular subsystems are proposed as descriptors of their information bond “order” and its covalent/ionic composition. These predictions are compared with the bond indices resulting from the molecular orbital (MO) theory. The rules for combining the subsystem entropy/information data into the corresponding global quantities describing the system as a whole are derived and tested. The so-called complementary reductions are used to formulate the exact combination rules for the molecular entropy/information bond indices. Applications to the three-orbital model and π-bond systems (butadiene and benzene) in the Hückel theory approximation are reported and used to illustrate the proposed concepts and techniques. The subsystem bond-order conservation and a competition between its ionic and covalent contributions are discussed. In contrast to the familiar MO bond indices, the entropic descriptors of molecular fragments are shown to exhibit a remarkable degree of equalization, thus emphasizing the information equilibrium of the ground-state distributions of electrons.