3 May 2013
Venue: GO Jones Room 410
van der Waals interactions: basic concepts and applications to nanostructures
John Dobson, Griffith University, Australia
This talk will first introduce some simple ideas that are helpful in understanding van der Waals / dispersion / Casimir forces from the Condensed Matter viewpoint. Various approaches for the prediction of these interactions will be discussed and compared, with some emphasis on methods based on response functions and relevant to extended nanostructures where simple pairwise additive methods are not reliable. In particular the Adiabatic Connection Fluctuation Dissipation (ACFD) approach will be introduced and related  to other methods such as the Lifshitz approach. Attention will also be given to "seamless" methods in this class, valid right down to intimate contact of the interacting objects: these include correlation energy calculations within the direct Random Phase Approximation d(RPA) and beyond. Finally if time permits a new approach within the ACFD scheme will be described, one that leads  to new implicit "third rung" correlation energy functionals with good van der Waals properties.
 John F. Dobson and Tim Gould, J. Phys. Condens. Matt.Matter 24, 073201 (2012)
 Tim Gould and John F. Dobson,Phys. Rev.B 84, 241108(R) (2011)
Get Real: Van der Waals Interactions in Complex Materials
Alexandre Tkatchenko (FHI, Berlin)
Van der Waals (vdW) interactions are ubiquitous in molecules, condensed matter, and hybrid organic/inorganic interfaces. These interactions are inherently quantum mechanical phenomena that arise from concerted fluctuations between many electrons within molecules and materials. We have recently introduced efficient methods that accurately describe the long-range many-body vdW energy for molecules and materials [PRL 102, 073005 (2009); PRL 108, 236402 (2012); PNAS 109, 14791 (2012); PRL 108, 146103 (2012)]. In this tutorial, I will survey our current understanding of vdW interactions and demonstrate that collective (many-body) vdW contributions can significantly exceed the highly coveted ``chemical accuracy'' for molecules and materials. We also provide a microscopic explanation for recent experimental observations that vdW interactions act at much longer distances than typically assumed. Our findings suggest that inclusion of the many-body vdW energy is essential for obtaining quantitative and sometimes even qualitatively correct results in materials modeling. Despite this encouraging progress, many challenges remain toward a universally applicable method for the modeling of vdW interactions, particularly for metallic, ionic, and low-dimensional materials.