(This is a joint colloquium sponsored by the School of Physics at Georgia Tech and the Department of Physics and Astronomy at Georgia State) Van der Waals Interactions from a Density Functional Perspective Walter Kohn Nobel Laureate University of California Santa Barbara With the help of time ? dependent DFT Van der Walls interactions between two non-overlapping systems A and B can be calculated for arbitrary geometries and chemical compositions. In particular, the traditional requirement in multipole expansions, that the distance d between A and B must be large compared to their characteristic dimensions, RA and RB, is found to be unnecessary. A new perspective, of Van der Waals interactions being due to the exchange of scalar potential waves, emerges. Applications, both completed and projected, will be presented. Refreshments will be served in the lobby in front of lecture hall at 3:30 p.m.