One way to accomplish this is to transfer accessible accurate results for small (diatomic, triatomic, etc.) fragments to larger systems through physically-based models, e.g. by means of a diatomics-in-molecule-like treatment using effective atom-atom potentials accounting for many-body distortions of pair interactions within the system. Transfer of these ab initio-calculated distortions to reliable empirical diatomic potentials has proved to be capable of accurately reproducing experimental data (within their uncertainties) for a series of triatomic systems, with no fitting or with a minimal scaling.
Such approach is particularly suitable for aggregates of rare gas atoms with molecules. A molecular system embedded in a rare gas solid or cluster matrix may behave differently from when it is free. The dopand can remain chemically unaffected due to inherent neutrality of the environment, which, however, may change activation barriers for different channels. Usually unstable systems can survive in the matrix for long enough to be investigated and/or to lead to chemical reactions and products not occurring under usual conditions. Cluster surroundings may influence reaction probabilities also by favouring reactant and product locations in the bulk or surface of the cluster and their specific orientations. To theoretically analyse such processes, reliable potential energy surfaces (PES) for the interactions of rare gas atoms with big molecules and their smaller fragments are required. These PES, in particular together with corresponding dipole moment surfaces, are directly applicable to interpretation of experiments on nonreactive such complexes and can be tested in such a way.
Logical extensions of such studies involve interactions between molecules (in particular within rare gas clusters and solids), pure and doped/mixed molecular clusters, interactions of molecules with solid (metal, semiconductor, etc.) surfaces, molecular assemblies in the surface and bulk of rare gas and other clusters and solids.
Clusters of open-shell atoms can be bound strongly and may preserve their integrity within aggregates of clusters. As intermediates between molecules and bulk matter, clusters can have properties different from those of both these limits. The new properties may thus possibly be transferred to cluster-assembled materials. Of particular interest are structural, optical, and electric properties of clusters and ordered nanostructures, molecular interfaces (metal :polymer, semiconductor :organic (bio-) molecule, etc.), including those relevant for quantum conductors (wires) and mesoscopic systems (devices) as building blocks for prospective molecular (nano-) electronics and photonics.
Yet another related area is a combination of quantum (accurate) and classical (efficient) theories for studies in spectroscopy and dynamics. A proper connection between the two ideologies and correspondence between their entities allow for reliable treatment of polyatomic systems and promise to help clarify, in particular, such issues as difficulties of semiclassical theory in the turning point regions, and relaxation of (quantum) zero vibrations in classical theory.