Theoretical chemistry represents a very different approach to the solution of chemical problems. It is probably most helpful to view research in the area of theoretical chemistry as being similar to research involving any of the more familiar experimental tools, such as the various spectroscopic techniques.

In the last twenty years theoretical methods have been refined to the point where calculations can determine molecular shape, vibrational spectra, dipole moments, quadrupole moments, photoelectron spectra, the relative stabilities of isomers and similar compounds, and even detailed information about reaction mechanisms. In a number of cases, the information obtained from theory is more accurate than that available from experiment. Naturally though, much of the best work comes when theory and experiment combine together. The application of theory has limitations which are different from those applicable to experimental techniques in that accurate theory is limited to the investigation of small molecules. However, there is a strength which cannot be matched in experiment, which lies in the ability to treat unstable, reactive species with the same ease as stable compounds.

The technique requires the solution of Schrodinger's equation to yield a wavefunction from which the properties of the molecule can be obtained. The advances of recent times have resulted in powerful computer programmes which carry out these steps. While the pain of obtaining the wavefunctions has been removed, honours projects in this area require that some considerable expertise in the quantum theory of chemistry needs to be acquired, so that the computer programmes can be used intelligently and meaningfully. With this knowledge there are many problems in chemistry which can be investigated in more detail than can be achieved by experiment.

Examples of problems which are of current interest are given below.

The chemistry and structure of small inorganic molecules is a major activity. Specific current interests are:

1.Small molecules composed of early elements in the periodic table. The most recent work has centred around S,N molecules such as S4N2 and C2O2, C2S2 and C2OS where the potential energy of the surfaces are being explored in detail with both ab initio and density functional techniques.

2.Transition states in sulfoxide chemistry.

3.General theories which can predict the shapes of molecules. Current work on the area is related to cycloprofenes and to a theory developed by Bunslett as it relates to the structure of clusters of four heavy atoms.

4.In collaboration with Dr G. A. Koutsantonis there is an interest in small metal containing molecules such as GaAs, GaP and InH3, the stability of analogues of N(BH2)3, the nature of bonding in compounds containing the M-Cº C-M grouping and the nature of so called metal-metal multiple bands.

In collaboration with Professor B. N. Figgis both experimental and theoretical investigations of spin and charge density distributions in transition metal complexes are being carried out. This involves single molecule and solid state calculations on the complexes, and formal development of methods for dealing with spin-orbit coupling, the orbital contribution to the molecular magnetisation and the applicability of unrestricted methods to determining small effects such as spin polarisation. Projects in this area are available.