Partitioning the electron number, pair and transition densities of silanes: An atoms in molecules study of the properties of silicon compounds

Abstract

<p>The field of silicon chemistry has proven to be an ever-expanding subject of interest in both the academic and industrial fields. A large portion of this work involves computational and theoretical studies of electronic structure. These studies use Molecular Orbital theory to obtain results which closely correspond with experiment. It is not enough, however, to know the properties of the molecule as a whole, frequently, important insights can be gained by understanding the contribution of an atom in that molecule to those total properties. While invaluable for computing the properties of an entire molecule, molecular orbitals contain no information about individual atoms, requiring the development of arbitrary mathematical treatments that partition the molecular orbitals according to their basis function expansions. The theory of Atoms in Molecules removes the need for arbitrary models by partitioning the molecular properties on the basis of the topology of the electron density, a method based on established quantum mechanical principles. This work began with a detailed analysis of the bonding and atomic properties of simple compounds containing silicon, with the analogous carbon compounds used as a comparison. This initial study illustrated why silicon species react the way they do, and how the electronic differences between silicon and carbon species result in differences in chemical properties. This work also studied the localization of electron density in silicon compounds using the pair density to further illustrate the nature of silicon's electronic structure. The focus of the study then shifted to oligosilanes, known to undergo strong electronic excitations that experience a bathochromic shift with increased chain length. Attempts to determine the nature of this so-called σ-conjugation made use of the electron and pair density properties, and finally the transition density, which allows one to partition the probability of excitation into its atomic contributions.</p>