5 SCIENTIFIC HIGHLIGHT OF THE MONTH Calculation of Dispersion Energies

”Dispersion forces” [1], [2] are generally understood in the solid-state physics community to be that part of part of the non-covalent van der Waals (vdW) interaction that cannot be attributed to any permanent electric mono-or multipoles. (In the chemistry community, the whole of the non-chemically-bonded interaction is often termed the ”van der Waals” (vdW) interaction, but in the the physics community this term is usually reserved for the outer dispersion component as defined above. A useful categorization of the many components of the total force is given in [3] from a perturbation theory standpoint). The ubiquitous dispersion forces occur wherever polarizable electron clouds are present, and are typically weaker than ionic and covalent bonding forces, but are of longer range than the latter, decaying algebraically rather than exponentially with separation. They are important in protein interactions, in rare-gas chemistry and in soft condensed matter generally. They are especially important, for example, in the cohesion and self-assembly of graphenic nanostructures including nanotubes and planar graphene-based systems, which have attracted strong recent interest in the condensed matter community. Much work has been done on the vdW interaction in the two extremes of (i) small molecules (via high-level quantum chemical methods such as coupled cluster (CCSD(T)) [4] or Symmetry adapted Perturbation theory (SAPT) [3]) and (ii) well-separated macroscopic objects (via Lifshitz theory and its extensions, for example [5], [6], [2]). However the study of vdW interactions between solids and nanostructures down to intimate contact, where dispersion competes with other forces, is still an area of active research. The selective adhesion of graphene to various metal substrates is an example of a delicate phenomenon where vdW forces are important but where a successful fully quantitative theory seems still to be lacking. This paper will outline the development of simple and more complex theories to account