Analysis of chemical bonding by means of reduced density matrices

Abstract

The modern Theory of Chemical Bonding may be well understood as the study of reduced density matrices (RDMs) in real space regions to get new insights of the chemical bond. Although, much work has been widely used to understand chemical bonding from one-electron density, include correlation effects requires the access to higher order densities. Based on the cumulant expansion of the RDMs, a set of bonding indices which may decomposed into one-electron component may be defined. Each component is partnered with a one-electron function(natural adaptive orbital, NAdO). Additionally to correlation effects, the renewed interest on long-range interactions, has moved chemists to developed new tools for understanding these interaction. NCI analysis has been arose as one of the most accepted index for exploring noncovalent interactions. Recently, it was shown that ionic interactions may be grasp by NCI index, but not much work has been carried out to understand the behavior of NCI in covalent bonds. In the present work, a comparative NAdOs and NCI analysis of the a set of small molecules has been carried out. As example of long range interaction, we examined the validity of the NCI index to analysis the bonding in a self assembly monolayer (SAM) of octylamine.