Professor Kazuo Takatsuka of University of Tokyo, Japan, visited University of Hyderabad during February 14-16, 2013 and delivered a seminar lecture in the School of Chemistry Seminar hall on February 15. He is an eminent theoretical and computational chemist. Among many diverse areas of the subject that he works on, in his lecture he focused on a unified theme of treating nuclear motion in molecules of chemical and biological interest beyond the celebrated approximation of Born and Oppenheimer (BO) in quantum chemistry.



The lecture started with a discussion on the validity of this approximation considering hypothetical mass combinations of fundamental particles and the typical error that one makes when the nuclear motions is followed on a single adiabatic electronic state. This BO approximation breaks down when more than one electronic states becomes energetically close and often intersect. Conical intersections of electronic energy surfaces are natural outcome in the latter case. He showed that the bifurcation of wave packet becomes a regular phenomenon in such a situation and the elecronic wavefunction developes a node so as not to go around the intersection point in a close loop to retain its single-valued property. While he focused on a full quantum mechanical treatment of nuclear dynamics for small molecular systems including interaction with radiation field, he discussed on a semiclassical treatment of the dynamics of systems of growing sizes. The latter relied on modified  trajectory surface hopping approach and he applied the technique to elucidate the proton transfer mechanism in biological systems.