The types of silicon–oxygen bonds from the perspective of descriptors based on one-electron potentials

Abstract

The properties of multicomponent compounds are determined by the types and characteristics of chemical bonds, enabling the study of the nature of interatomic interactions in different phases of matter: from gases to solids, including a crystal phase. Copolymers based on polydimethylsiloxanes are widely used because of their chemical resistance, relative inertness, and ability to spontaneously restore their initial structure through a self-healing process after defect formation. This is experienced due to the so-called “siloxane equilibrium” phenomenon, in which the O–Si bond in a polysiloxane chain can dissociate to form the anion that can attack another chain leading to crosslinking and dynamic chain exchange. Since the ability for self-healing mainly depends on the formation of both covalent and noncovalent bonds; it is essential to develop quantitative criteria for the identification of the bond types in multiscale models. Therefore, the main goal of this study is to analyze the electronic descriptors for classifying different types of silicon-oxygen bonds. For this purpose, we have modeled and analyzed various molecular and crystal structure models containing O–Si/O...Si bonds of different types. These bonds were categorized using electronic descriptors previously developed within the framework of the orbital-free density functional theory (OF-DFT) and based on one-electron potentials. One of these descriptors involves the comparison of the gaps between the positions of 1D extremes in electron density, electrostatic potential and total static potential functions along the interatomic line, which makes it possible to identify covalent bonds, coordination bonds and weak noncovalent interactions (or the tetrel bonds, TtB). The aim of our research is to determine the applicability of the electronic criterion and evaluate descriptors which enables identification of strong covalent (O–Si) or coordination bonds and weak (O...Si) noncovalent interactions in various systems containing silicon–oxygen interactions. We have started by analyzing the absolute difference between the positions of extremes in electronic functions, which have allowed the identification of bond types. Next, we have analyzed the features of identical compounds in different phase states that affect the electronic structure and descriptor values, and also determined the impact of the formal charge on the values of electronic descriptors.