Modelling of electronic structure

The established methods for calculating the accurate electronic structure of small molecules are now being extended to cover larger systems of particular importance in molecular design. New areas include calculations on an expanding range of large molecules, the understanding of intermolecular interactions relevant to molecular recognition in biological systems and the reliable prediction of solvent effects. Since the first accurate, or ab initio molecular orbital (MO) calculations were done on simple diatomic molecules such as lithium hydride some 25 years ago, the range of molecules that can be described by accurate MO methods has expanded rapidly. Such calculations are now making an increased impact on diverse areas of chemistry. In this article we will review the current use of strictly ab initio MO methods in the study of large molecules.