Theoretical Approaches to the Study of Non-Bonded Interactions

There have been two main approaches to modelling the weak intermolecular forces between closed shell molecules for simulating the properties of the molecular solid, liquid and gas. Quite detailed model intermolecular potentials, specific to each molecule, are used for small polyatomics, such as HF, Cl2 and water. These model potentials are often derived, at least in part, from ab initio calculations, and are tested for their ability to reproduce the spectra of van der Waals dimers or molecular beam experiments as well as condensed phase simulations. In contrast, the models for intermolecular forces used to simulate organic and biochemical interactions are mainly derived by assuming that each intermolecular atom-atom interaction is transferable between different molecules. Such models are usually derived empirically, by fitting to a range of experimental data such as molecular crystal structures. Such model potentials are now used to improve our understanding of biochemical interactions, including drug design. The realism and reliability of such simulations depends fundamentally on the accuracy of the model for the intermolecular forces, and thus we seek more accurate model potentials for organic molecules. Most of the recent progress towards this goal has come from extending the ideas and techniques, which are used to develop accurate potentials for small polyatomics, to larger molecules.