Spatial partitioning of the molecular wave function: Reexamination of the bond-charge model of covalent binding

摘要

Owing to the complexity of many-body quantum interactions, theoretical problems in chemistry almost always necessitate numerical methods of solution. In turn, and somewhat paradoxically, this reliance on computation often precipitates a need for approximate models that can provide a conceptual framework for the interpretation of the accurate numerical solutions. In this report, we reexamine and improve upon the simple bond-charge (SBC) model of Parr and Borkman with the express purpose of examining its role as a suitable intuitive model for bonding energetics. We first discuss the role of spatial partitioning in the SBC model and the molecular-structure approximations that are implicit within the model. We then develop an improved version of the model by including electrostatic repulsion between shared electron pairs; we refer to this enhanced version as a semiempirical charge-cloud (SCC) model. Applying the SCC model to a broad range of diatomics, we find that it is able to predict dissociation energies on a par with simple variational calculations. As an illustrative application of the SCC model, we use it to estimate unknown dissociation energies and rotational constants for a number of alkali dimers. (C) 2004 Wiley Periodicals, Inc.